Outlook Invite Sent to Wrong Person

Hi All,

I have a problem where an Outlook Invite is sent to User A (usera@company.com), and straight after it’s sent I get a bounce back saying that it was undeliverable. However when I look at the address in the undeliverable email, it is completely different to User A, for example it will say User B (userb@company.com). Even so, User A still receives the invite

The bounce back email always contains the same incorrect user. If I send a normal email to User A, the email is sent without any problems, and there are no bounce backs.

Any ideas?