Email doesn't get send from TrueNAS - Broken pipe

[sce91]

As the title says, I don't receive email notifications about the status of my TrueNAS.
I'm running TrueNAS core 12.0-U1, have setup email alerts using Gmail Oauth, and when hitting the 'Send test email' button I do receive a test email.

/var/log/maillog:

Code:

Mar 26 00:00:03 freenas 1 2021-03-26T00:00:03.506101+01:00 freenas.local /middlewared 15252 - - Failed to send email to my-email@gmail.com: [Errno 32] Broken pipe
Mar 26 00:01:00 freenas 1 2021-03-26T00:01:00.034843+01:00 freenas.local /middlewared 15252 - - Failed to send email to my-email@gmail.com: [Errno 60] Operation timed out
Mar 26 00:01:37 freenas 1 2021-03-26T00:01:37.240276+01:00 freenas.local /middlewared 15252 - - Failed to send email to my-email@gmail.com: [Errno 32] Broken pipe
Mar 26 14:29:22 freenas 1 2021-03-26T14:29:22.246148+01:00 freenas.local /middlewared 15252 - - Failed to send email to my-email@gmail.com: [Errno 32] Broken pipe

Does anyone have a clue of what could be going on here?