on a website I use PHPMailer to send automated registration emails, etc and also a newsletter-tool (which loops through the emails and sends them one by one).

Also, I configured in Gmail under Settings and confirmed @mydomain addresses, so I can send from @mydomain emails without the gmail address being displayed.

Furthermore I authorized the website to send mails with this link: https://accounts.google.com/DisplayUnlockCaptcha

Now, after 2 month where everything worked perfectly fine, suddenly users started not to receive emails anymore and most recently emails are not even being sent anymore.

Also, I received many error messages like this:

Technical details of permanent failure:

Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 5.4.1 [email protected]: Recipient address rejected: Access Denied (state 13).

When I check at this link: https://toolbox.googleapps.com/apps/checkmx/

It tells 2 none critical errors:

• Relayhost configuration detected.
• There SHOULD be a valid SPF record.

So, the questions I would have were:

• does anybody have any hint why it stopped working, what the error messages mean?
• what to do to fix it?
• where do I set a SPF record (Cpanel?)?
• what is a relayhost and how to fix that?

It is about 1000-1400 mails a day (gmail's limit is 2000). Also, what can I do wrong when setting up an SPF record? I've heard there are some testing tools for that.

Thank you so much already in advance for your help!