We synchronized our outlook account with Zoho.

Some of the mails are not being received 

We noticed that this happens when 2 different mails have the same subject

Could be the Anti-Spam feature be causing this?

How we disable it (We tried to disable it on setttings, presents a message that the antispam has been disabled but when checking it back it hasn't changed from enabled to disabled.

No button visible to "save" the state

Please advice

Regards,