Emails sent to gmail addresses from my email address based on my own domain are blocked

Question

Hello. On both the IPad and Android phone, I can send emails to all addresses except gmail addresses if I have the From address based on my own domain (me@my domain.co.uk). If I use a From address based on zen.co.uk, the messages sent to gmail addresses get through.
Is Gmail blocking me@my domain.co.uk and, if it is, how do I stop this happening? I’ve read stuff about verification with Postmaster by adding text to DNS, but I’ve no idea what this means or how to do it.
On the IPad, I’m using Mail; on the Android, I’m using TypeApp

bkennelly · Accepted Answer

It looks like you have a good SPF record now.  If they support it, make sure you set up DKIM, too.
It isn't just for Gmail, but they are getting more aggressive about requiring some form of sender verification.  Expect more of the same from other email providers.

bkennelly · Accepted Answer

In a previous response, you stated that you send all mail through Zen.co.uk, so they are your email provider.  You need an SPF record In your DNS to let other email servers know that messages from your domain, coming from Zen, are good.
From everything you have written, it sounds like your SPF record should be:
"v=spf1 include:_spf.zen.co.uk ~all" 
You need to replace the existing SPF record with this one.  If you do not know how to update your DNS, you need to contact your DNS provider (Ionos?).  I also recommend double checking with Zen about the SPF.

bkennelly · Accepted Answer

I just looked up your domain's TXT records and examined the result, but there are some useful tools, like MXtoolbox:
https://mxtoolbox.com/spf.aspx