Google (gmail) recently seems to reject legetime emails if no SPF record (URL: https://de.wikipedia.org/wiki/Sender_Policy_Framework) is set for the domain of the sender address.
A sender in such a case receives an error mail back with the following message:

SPF check for [your-domain.tld] does not pass with ip

To prevent your mails from being rejected by Google mail servers, an SPF record must be set.

If you use our mail servers, the following include can be used:

include:_mail-out.iphh.net

If you send your emails exclusively through IPHH mail servers, the SPR record can look like this:

"v=spf1 mx include:_mail-out.iphh.net ~all".

If you send e-mails via other servers as well, these servers must also be listed in the SPF record.

It is important that an SPF record is complete and correct. Otherwise e-mails may be incorrectly marked as spam or rejected.

If you have any questions or need advice, please contact our support at any time.