FINAL WARNING :: Need immediate action
No, I'm not threatening you!

That is just the subject of an email I received from noreply@zoho.com. The email text was:
"Dear <zoho_email_address>,
Problem while forwarding mails to <gmail_email_address>. Repeated failure will disable email-forwarding.
Regards,
Zoho Mail Mail Administration
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This is an automated message, please do not reply
"
Of course I changed the actual email addresses to avoid unnecessary attention.
This email arrived after a previous similar warning. The problem is I don't have a clue (nor the email text helped me have one) about why this is happening.
I have several zoho email addresses forwarding to the same gmail account without an issue, so I don't see why this one shouldn't work.
Please shed some light on the matter, and of course I'll be more than willing to cooperate with you to solve the issue.
Thanks for the support and for what - so far - looks like a very professional suite.
-Gabriele