folder cannot be accessed by IP

[studio4host]

check that your dns is resolving and also check if you have enabled this function in the mail server manager "Reject Unknown Hostname (NOT recommended):" and disable it if you have it enabled.

host google.com

[studio4host]

you simply need to rebuild mail server and edit configuration to have less security check if you want to speed it up, however, this issue is probably related with your server provider as they scan your emails.