sendmail does not like one user

Wed May 3 22:18:32 UTC 2006

Hey guys,

sendmail-8.12.11-4.21AS.8 on rhel-2.1, having a strange problem:

userA at mycompany.com sends email to userX at partnercompany.com just fine.
userB at mycompany.com, though, cannot send email to userX, his messages
get bounced with a delayed Status: 4.4.1. messages from userB to other
places go through fine. if userB uses our CRM to send email to userX,
it goes through fine as well.

no clue where to begin working on this.

Any clues are appreciated.

Thanks,
G