What are Apple Mail blocks?
Apple Mail supports the email domains of @icloud.com, @me.com, and @mac.com. All three of these mailboxes are notoriously awful for allowing email to be delivered.
When sending email from VipeCloud, we are lucky enough to see that he email bounced (when sending from your personal email you are often ot made aware). When Apple bounces an email the error is:
550 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137
How to fix Apple Mail blocks?
Ask your recipients to add a rule in Mail > Preferences to allow/whitelist email received from your sending domain. (If your email is a generic @gmail.com, @yahoo.com, @hotmail.com etc have them whitelist vipe.vcmsr.com.)