Set up rules for attachment compliance
As a G Suite administrator, you can set up compliance rules for message attachments, such as documents, video and sound files, images, and compressed files and archives. Rules specify conditions based on file type, file name, and message size. They also specify how to handle messages that meet the conditions.
The following actions can be taken on a message that contains an attachment:
- Reject the message
- Quarantine the message and attachment for review
- Modify the delivery of the message and the attachment
You can also set up a rule to detect encrypted attachments. This distinction can be useful if you need to send unencrypted copies of message attachments to an archive server for regulatory purposes.
How attachments are scanned
Gmail supports binary file-type detection for pre-defined and custom file types, which helps prevent people from circumventing attachment rules by renaming extensions. Files are scanned based file type, for example doc. Gmail scans the filenames of files inside archives, including encrypted archives and nested non-encrypted archives. However, the inner archives of an encrypted archive cannot be scanned.
How settings are applied
Unless modified in the Options section, the setting applies to all users in an organizational unit. Users in child organizations inherit the settings you create for the parent organization. Inherited settings can be disabled in child organizations, preventing the disabled setting from applying to the child organization, as well as it's grandchild organizations. You can also add multiple settings to each organization.
Enhance message security with hosted S/MIME
You can enhance message security using advanced features for Secure/Multipurpose Internet Mail Extensions (S/MIME). For example, you can set up a rule that requires the use of S/MIME encryption for outgoing messages. You set this up with the Encryption option, described in Step 3.
For an overview, see Enhance message security with hosted S/MIME.
Set up an attachment compliance rule
Initial step: Go to Gmail advanced settings in the Google Admin console
From the Admin console Home page, go to AppsG SuiteGmailAdvanced settings.
Tip: To see Advanced settings, scroll to the bottom of the Gmail page.
Scroll to the Attachment compliance setting in the Compliance section, hover over the setting, and click Configure. If the setting is already configured, hover over the setting and click Edit or Add another.
For each new setting, enter a unique description.
Go to the next step to configure the setting.
Step 1: Enter email messages to affect
Check the boxes next to the messages you want the rule to apply to.
Go to the next step to continue.
You can add up to 10 expressions. Each expression must individually added and saved.
From the list, specify whether any or all conditions must match to trigger what happens to the message. For example, if you select If ANY of the following match the message, any matching condition can trigger the consequence to the message.
From the list, choose what you want to specify for the expression:
File type—Select the attachment types to include. You can also enter a custom file type to look for matches based on that file type.
Note: For your protection, file types that are considered to be executables are automatically rejected. To see a complete list of extensions, see File types and extensions supported in expressions.
File name—Enter an attachment name that you want to include. Any part of an attachment file name is returned as a match, whether it's upper or lowercase.
Message size—Enter, in megabytes, the size limit for messages. The size includes the message body and all attachments. (This is the raw size of the entire message, which may be up to 33% larger than the native size of the message and attachments due to normal encoding overhead.)
Click Save. You might need to scroll to see it.
Go to the next step to continue.
Step 3: Specify what happens if expressions match
Specify whether to modify, reject, or quarantine a message when conditions are met. (Details below.)
Configure the options for the actions you choose.
(Optional) Click Show options to configure additional options to limit the application of this setting. See Configure additional parameters, below, for details.
Go to Save the configuration.
Rejects the message before reaching the recipient. You can enter a message to notify the sender about why the message was rejected. For matching messages, no other routing or compliance rules are applied; the message is simply rejected.
Note: Gmail automatically adds an SMTP rejection code, such as 550 5.7.1. This is a requirement of the SMTP standard and can't be deleted.
Sends the message to an admin quarantine where you can review the message before deciding to send it or reject it. Available only for the Users account type. See Account types to affect below.
To notify your users when their sent messages are quarantined, check the Notify box.
You can modify messages by doing things like adding headers, removing attachments, changing the envelope recipient, adding more recipients (additional or secondary routes), and changing the route.
Note: We recommend that you use the routing settings for the specific use cases they are intended to support. For example, you can set up the same routing options by using an Attachment compliance setting or a Routing setting. Use an Attachment compliance setting for attachment-related use cases, and a Routing setting for general routing-related use cases, such as dual delivery. Learn about mail routing, including use cases and examples.
Add X-Gm-Original-To header
Check this box to add a header tag if the recipient is changed. That way, the downstream server will know the original envelope recipient. An example of the header tag format is
Headers are useful if you're rerouting a copy of the message to another recipient. In this case, you're changing the recipient address, but the new recipient can still see the address of the original envelope recipient. They can see the original envelope recipient by checking the
X-Gm-Original-To header in the message.
Add X-Gm-Spam and X-GM-Phishy headers
Gmail messages are automatically filtered for spam and phishing. Check the Add X-Gm-Spam and X-Gm-Phishy headers box to add these headers to indicate the spam and phishing status of the message. For example, an administrator at a downstream server can use this information to set up rules that handle spam and phishing differently from clean mail.
X-Gm-Spam: 0indicates the message isn't spam.
X-Gm-Spam: 1indicates the message is spam.
X-Gm-Phishy: 0indicates the message is not phishing.
X-Gm-Phishy: 1indicates the message is phishing.
Any message marked phishy is automatically marked spam as well.
If you add X-Gm-Spam and X-Gm-Phishy headers to your messages, consider where the message is being routed to next. A rerouted message is often no longer classified as spam when it reaches its destination because elements of the message, such as the sending IP address, have changed.
If your messages are rerouted to your downstream server, set up rules on that server to read these headers and prevent messages with
X-Gm-Spam: 1 or
X-Gm-Phishy: 1 tags from being delivered to users’ inboxes.
Note: If the Account types to affect is set to Groups, the X-Gm-Spam and X-Gm-Phishy header tag values are always set to 0. See Account types to affect, below, for information on the account types.
Add custom headers
You can add one or more custom headers to messages that are affected by this setting. For example, you can add a header that matches the description that you entered for the setting. Doing this can help you analyze why a message was routed in a certain way or why a rule was triggered.
Prepend custom subject
You can enter a string to prepend to the subject of applicable messages. The string will appear in brackets at the beginning of the subject. For example, you could enter Confidential in this field for sensitive emails. If a message triggers the rule and its subject is Monthly report, recipients will see the following subject: [Confidential] Monthly report.
Change route and Also reroute spam
Change route—Changes the destination of the message. By default, the Gmail server is the primary delivery location. However, you can change it to route messages to a different mail server, such as Microsoft® Exchange.
Note: Before you can change the route, you need to add the route using the Hosts tab. After it's added, it'll appear in the Change route list.
Also reroute spam—Appears if you select Change route. Also reroute spam lets you route all email that matches the criteria of the setting, including messages marked as spam.
If you don't check the Also reroute spam box, then normal messages are rerouted, but spam messages aren't.
Whether or not you select Also reroute spam, blatant spam is not rerouted because it’s dropped instantly at delivery time.
If a message is classified as spam but one of the G Suite email settings overrides it (for example, due to a sender whitelist), then the message isn't considered to be spam for this purpose and it's routed as a normal message.
Change envelope recipient
You can change the envelope recipient in one of the following ways:
To replace the recipient’s entire email address, after Replace recipient, enter the full email address, such as firstname.lastname@example.org.
To replace just the username of the recipient's email address and keep the domain the same, before @existing-domain, enter the username, such as user.
To replace just the domain of the recipient's email address and keep the username the same, after existing-username@, enter the domain, such as solarmora.com.
Changing the envelope recipient for a message on the primary address is equivalent to forwarding a message to a different recipient. The message bypasses the original recipient’s mailbox and is routed back to the internet for delivery to the new recipient. The To: address remains the original recipient address, even though the envelope recipient is replaced.
The destination server is determined by an MX lookup on the new recipient's domain. Or, if you’re using the Change route control, the destination server determined by the specified route.
If you'd rather Bcc an additional recipient, use the Add more recipients option, described below.
Bypass spam filter for this message
Check this box to deliver incoming messages to recipients even if the spam filter identifies them as spam. This option applies to incoming messages only—you can’t bypass spam filters for outgoing messages.
Note: This option applies to the Users and Unrecognized / Catch-all account types, and not the Groups account type. See Account types to affect, below, for information on the account types.
Remove attachments from message
Check this box to remove any attachments from messages. Optionally, you can append text to notify recipients that attachments were removed.
Add more recipients
Check the Add more recipients box and then click Add to set up dual delivery or multiple delivery.
Select Basic from the list to add individual email addresses and then click Save. Click Add to add more addresses.
Select Advanced from the list to choose advanced options for your secondary delivery. Similar to the settings for primary delivery, you can change the envelope recipient, add headers, prepend a custom subject, and remove attachments for secondary deliveries.
A limit of 100 additional recipients applies for each rule. For this reason, consider using groups for large lists.
Any settings that you configure for the primary delivery also affect the secondary deliveries. For example, if you change the envelope recipient, prepend a custom subject, and add custom headers to the primary delivery, the same configuration is applied to the secondary deliveries. If you change the envelope recipient, the To: address still remains the original recipient address.
For secondary deliveries, the Do not deliver spam to this recipient and Suppress bounces from this recipient boxes are checked by default. If the message is spam, this option discards the copy of the message being sent to the additional recipient. Suppress bounces from this recipient prevents bounces from going back to the original sender.
Encryption (onward delivery only)
By default, Gmail always attempts to deliver messages using secure transport (TLS). If secure transport isn’t available, the message is delivered over a nonsecure connection.
Check the Require secure transport (TLS) box to include secure delivery as part of content compliance for outbound messages. This requires all messages meeting the conditions in the setting (such as match expressions, account types, and envelope filters) to be transmitted via a secure connection. If TLS isn't available on the sending or receiving side, the message won't be sent.
Check the Encrypt message if not encrypted (S/MIME) box to make sure that certain messages can’t be sent unless they are S/MIME encrypted. See note below.
Also check the Bounce message if unable to encrypt box to bounce messages that aren’t S/MIME encrypted.
Learn more about enhancing message security with hosted S/MIME.
Configure additional parameters (Optional)
Click Show options to configure additional options for this setting.
You can specify address lists as a criteria for whether to bypass or apply a given attachment compliance rule. These lists can contain email addresses, domains, or both.
To determine if the address list is matched, G Suite considers the "from" sender for received mail and the recipients for sent mail. For senders, the authentication requirement is also checked. (Details below.) If multiple lists are specified, the address must match at least one of the lists.
The options for whether to bypass or apply a given attachment compliance rule are:
- Bypass this setting for specific addresses / domains—Skips the setting entirely if the address list matches, regardless of any other criteria specified in the setting.
- Only apply this setting for specific addresses / domains—The address list match becomes a condition for whether the setting is applied. If there are other criteria in the setting, such as match expressions, account types, or envelope filters, those conditions must also match for the setting to be applied.
To create an address list:
In the Options section, check the Use address lists to bypass or control application of this setting box.
Select one of the options:
Bypass this setting for specific addresses / domains
Only apply this setting for specific addresses / domains
Click Use existing or create a new one.
Select the name of an existing list, or enter a custom name for a new list in the Create new list field, and then click Create.
Hover over the list name, and click Edit.
To add email addresses or domains to the list, click Add.
Enter a full email address or domain name, such as solarmora.com. Or, to add a list in bulk, enter a comma or space delimited list of addresses after clicking add.
Note: Check the Do not require sender authentication box to bypass the Content compliance setting for approved senders that do not have authentication, such as SPF or DKIM, enabled. Use this option with caution as it can potentially lead to spoofing.
To include additional email addresses or domains in the list, repeat steps 5 to 7.
When you're done, go to Account types to affect.
Account types to affect (Required)
Select one or more account types that the setting applies to. The account types are Users, Groups, and Unrecognized/Catch-all. You must select an account type before you can save the setting.
If you’re configuring the setting for the top-level organization and you select the Modify message or Reject message action, all three account types are available. If the action is Quarantine message, just the Users account type is available.
If you’re configuring a sub-level organization, the only available account type is Users.
The Groups account type doesn't apply to the Add X-Gm-Spam and X-Gm-Phishy headers control. If the account type is Groups, the headers are always
X-Gm-Spam: 0 and
X-Gm-Phishy: 0. The Groups account type also doesn't apply to the Bypass spam filter for this message control.
By default, Users is selected, but you can select more than one type. For example, you can configure an inbound setting that only applies to the Groups account type, and the group must be the recipient. If you’re configuring an outbound setting, the account type must match the sender.
When you're finished:
(Optional) Specify an envelope filter.
Go to Save the configuration.
You can choose to affect only specific envelope senders and recipients. You can specify a single recipient, a number of users using a regular expression, or email groups.
To set up an envelope filter, check the Only affect specific envelope senders box, the Only affect specific envelope recipients box, or both. Then, from the list, select an option:
Single email address—Specify a single user by entering one email address. It needs to be the complete email address and include @ and the domain name. The match is case insensitive.
Pattern match—Enter a regular expression to specify a set of senders or recipients in your domain. Click Test expression to make sure your syntax is correct. For example, you can ensure this setting applies only to 3 specific users by entering the list of users using the following regular expression syntax:
In the expression:
- ^ matches the start of a new line.
- (?i) makes the expression case insensitive.
- $ matches the end of a line.
Learn about using regular expressions.
Group membership—Select one or more groups in the list. For envelope senders, this option only applies to sent mail. For envelope recipients, it only applies to received mail. If you haven't, you'll need to create the group first.
When you're finished, go to Save the configuration.
Save the configuration
Final step: Add and save the setting
Click Add setting or Save. Any new settings are added to the Gmail Advanced settings page.
At the bottom, click Save.
The table below defines common and custom file types you can use in an attachment compliance expression. For your protection, file types that are considered executables are automatically rejected. Learn more about blocked file types.
- Common file types. By default, all common file types are matched by file format and filename to identify the type of content and the attachment's extension. Examples include image/photo.jpg or document/letter.doc.
- Custom file types. By default, custom file types are matched only by filename, for example, photo.jpg or letter.doc. To match custom file types to file format as well, check the Also match files based on file format box.