<firstname.lastname@example.org>: host gmail-smtp-in.l.google.com[***.***.***.**] said: 550-5.7.26 This mail has been blocked because the sender is unauthenticated. 550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM. 550-5.7.26 550-5.7.26 Authentication results: 550-5.7.26 DKIM = did not pass 550-5.7.26 SPF [lucaf.eu] with ip: [***.***.***.**] = did not pass 550-5.7.26 550-5.7.26 To mitigate this issue, please visit Gmail's authentication guide 550-5.7.26 for instructions on setting up authentication: 550 5.7.26 https://support.google.com/mail/answer/81126#authentication k33-**************************.*** - gsmtp (in reply to end of DATA command)
The error 5.7.26 is caused by Gmail’s Sender Policy Framework (SPF) requirement, which is not created by default for Hover’s email service. To fix the error, follow this guide and create a SPF record for your domain.
The record suggested in Hover’s guide fixed the issue for me.
v=spf1 include:_spf.hostedemail.com include:hover.com ~all