SMTP 503

Robert_Vilhelmsen

Hi,

Fireware 12.9.3

I am in the process of figuring out why some internal mails which are send out via O365 are not reach by the end user.

We have a payroll erp system which periodicly sends out hundred of e-mails via a simpel internal smtp through a Microsoft 365 smtp connector and in the middle is a WG smtp proxy.

All traffic is encrypted with tls 1.2 and the smtp proxy rule is Required * * Preferred.

Looking at the mail flow from the internal smtp log, i see maybe 5% of the messages getting error 503:

104.47.11.74 OutboundConnectionResponse SMTPSVC1 SERVERNAME - 0 - - 503+Bad+sequence+of+commands 0 0 28 0 2719 SMTP - - - -

104.47.11.74 are Microsoft but who is giving me the error 503. Is it Watchguard proxy or Microsoft?

Regards
Robert

james.carson

Hi @Robert_Vilhelmsen

I can't tell from that log what side for sure is generating that. I think the "OutboundConnectedResponse" suggests it's external to the firewall. A packet capture of both the external and internal traffic should make it pretty clear what side is generating that.

Robert_Vilhelmsen

Thanks