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:
184.108.40.206 OutboundConnectionResponse SMTPSVC1 SERVERNAME - 0 - - 503+Bad+sequence+of+commands 0 0 28 0 2719 SMTP - - - -
220.127.116.11 are Microsoft but who is giving me the error 503. Is it Watchguard proxy or Microsoft?