Outlook distributuon list e-mails are being blocked

some ISPs block as SPAM?

[skipfactor]

A resell client complained that he's missing mail when sent via Outlook distribution lists. I tested it locally delivering via several different hosts & received undeliverable errors for some recipients:

553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)

or

554 <[e-mail]>: Relay access denied

Anyone else getting undeliverables with simple distribution lists? My test list consists of 4 recipients, and I'm using plain text test mails.

[Mardi_Gras]

Do the same e-mails get through without problem when sent individually?

[skipfactor]

>>Do the same e-mails get through without problem when sent individually?

Yes