Hello! I will assume your emails include pictures or some form signature and links. The spam filter may intercept the e-mail if any part of the message is interpreted as spam. You could therefore try sending a message containing only text or even empty and without signature and see if it is received on the recipient's side. In some cases, we observed the issue could be resolved by re-doing the signature or links.
If the problem is generalized, checks must be completed by the responsible team. It would therefore be important to contact the technical support team and if possible, have an example of a message that was not received in order to verify if it's blocked. Ideally, the message sent should not be older than three days