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"The recipient server did not accept our requests to connect" from GMail after updating SSL/TLS cert 1 Recommended Answer 7 Replies 10 Upvotes
Last edited 7/21/19
On Friday, 19 July 2019, we updated the SSL/TLS security certificates out our mailserver (c4.net and associated domains.) After replacing the certificate, we noticed that mail stopped arriving from gmail.com and GApps-hosted domains. Senders from those domains received a message about a temporary delivery problem after 24 hours, saying the response from our server was:
The recipient server did not accept our requests to connect.
I've confirmed we have a clear path for traffic through our firewalls for traffic from all the servers listed in the _spf.google.com IP blocks, as well as confirmed that none of those IPs are blacklisted on our mail server, as well as the IP's being exempted from Greylisting.
We did change our Certificate vendor from COMODO to LetsEncrypt in this most recent update, which is the only significant change on our end. It did replace the by-now-expired certificate that was on SMTP 25. Is it possible GMail is rejecting a connection because of the CA on the certificate?
Note that our domains that do not use TLS on SMTP are not impacted by the issue, strongly implicating the certificate in this problem.
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