No idea, follow info please : https://support.mozilla.org/en-US/kb/forum-response-firefox-sync-verification-email-faq

Please let us know if this solved your issue or if need further assistance.

This did not work. I spoke to my mail service provider again and they said that when the firefox email server initiated the SMTP connection, my provider responded with a helo and an authentication banner indicating that the SMTP server requires authentication for login attempts. When the sending server received that banner, instead of ignoring it and initiating the mail transaction as it should, it would instead attempt to login to the mail server without any credentials, resulting in an immediate rejection and transaction termination. They were able to get me my verification email by creating a temporary policy that disabled the Authentication banner for that sender long enough for me to get the email, but since it is a security policy, they removed it once I got what I needed.

There are chances you won’t receive any emails, but those issues should be covered in the link / forum response provided by Pkshadow. The issue you described is apparently about the transaction between Mozilla’s email server (or an intermediate one, or most likely the one at amazonses) and the receiving server at your provider, so that would be interesting to know and verify and would provide an additional reason not covered in that response yet.

The amazonzes or one of their other servers may be blocked by your provider, so make sure to check your spam folder there, but it seems you have. It might be blacklisted at this point based on the SORBS DUHL blacklist (small chance), though they should filter that to your spam folder too rather than completely ignoring it. I understand they set up a policy with regard to the authentication banner, but perhaps you can ask them about that?

Also see this question.

I checked with my service provider on that as well. The blacklist concern was not only eliminated as a factor, but my email host confirmed the amazon servers are white listed.

Did you wait 24 hours between requests? Since it has been a few weeks, is this still happening?

If so, please PM me with your email and I can help open a bug report.