SMTP by Zapier error: 550, b`Requested action not taken: mailbox unavailable\nSender address is not allowed

Hi there @Felix Wetzstein,

Welcome to the Community! 🎉

Sorry to hear you're having trouble connecting SMTP. It looks like there may be an issue with the system sending the test email, which it does to confirm the connection.

Could you try entering the email from your SMTP account into the "From Email" field? It's indicated is "optional" but often entering in an address you want to send from will help with connection issues.

Kindly give it a try and let me know how it goes? I'll keep an eye out for your response!

Hi @xliu,

You might be using an unsupported port number.

• Zapier only supports either unencrypted (non-TLS on port 25/2525/etc), and encrypted TLS (STARTTLS over either port 465/587/etc) connections for SMTP. SMTPS over port 465 is not supported: https://help.zapier.com/hc/en-us/articles/8496305915917-Send-emails-in-Zaps#h_01HNZM5F5PTXNCZXP779NS3JYG

Hopefully, this helps.