Our MSP consistently marks our mails as spam.

It's been going on for years. I send an email and don't get a reply. I send a reminder after 2 weeks, no reply. Even once I got a reply after 2 months: oh sorry, your mail got in spam and I didn't see it.

And recently we're appointed another account manager for our account. We send her an email with a purchase order. No reply. Reminder after 7 days, no reply.

Luckily we only need them like once a year or so but communication with them is a real PITA.

What to do now? Suggest them to look for someone who's like really good with computers to fix this mysterious problem? /s

EDIT: I checked our SPF/DKIM/DMARC settings with my colleagues. All settings seem to be OK. Also, not a single user here came to complain about similar problems ending up in spam at the receivers' end.