Invitation emails not coming through to specific email accounts

[Matt Gonda]

I setup a business account with Trello a couple weeks ago without incident. I then added two members with their emails within the same domain as mine. They did not receive an invitation email. I tried re-inviting each 3-4 times. No emails. I then sent the invitation to their personal email. They received it instantly. 

I have run message traces in the O365 admin tools and do not see any emails from Trello.com, nor do I see anything being blocked as spam in quarantine (domain level spam folder). There's nothing in the individual email users' spam files. 

I tested their email accounts by sending them test emails from inside and outside the domain, and there were no issues.

Any ideas what is going on?

[Torben_trello]

Any chance that the initial emails were rejected by the mailserver? That would cause them to be blacklisted on our end. Feel free to reach out to trello.com/contact with those emails so we can check our logs.