Hi Michael. We discovered a similar problem when we moved to O365.

We fixed it by adding entries into the Active roles console for the

listname and owner-listname. This provides Listserv's IP address an

exception to O365 so all mails sent to listserv do not get processed back

thru O365 and instead go directly to the listserv for processing.

See examples below for a list called csaam.

Under General properties:

Under email addresses:

Hope this helps. Cheers.

Mignon Erixon-Merritt

Systems Software Specialist, OCIO

Smithsonian Institution

380 Herndon Parkway, Herndon VA 20170

202-633-6373

-----Original Message-----
Subject: O365 Migration Troubles

we are moving from an on prem exchange server to O365, and our listserv is one of the last things we need to move off of the on prem relay.
and we are really struggling to get our emails to flow through o365. When we send an email, i see it flow through the IIS SMTP service,

into the "Queue" folder, then it ends up in the "badmail" folder with the following error: