I may be wrong, but I believe this error message means that your primary email address either doesn't exist or didn't accept the email from the Firefox Account service.

To connect to Firefox Sync, you need to confirm through email in addition to signing in the regular way. Therefore, if your email on your account doesn't work properly, you won't be able to login to Firefox Sync until you get a functioning email address connected to your account.

Hope this helps.

Wesley Branton said

I may be wrong, but I believe this error message means that your primary email address either doesn't exist or didn't accept the email from the Firefox Account service. To connect to Firefox Sync, you need to confirm through email in addition to signing in the regular way. Therefore, if your email on your account doesn't work properly, you won't be able to login to Firefox Sync until you get a functioning email address connected to your account. Hope this helps.

This is where it doesn't make any sense. My email account is working as usual.

I'm not receiving any emails from mozilla about this and I've checked my spam/trash folders and my spam filters. I've received other newsletter type emails from mozilla recently too. I also went and made contacts for addresses from mozilla just to make sure. I just got an email notification from this forum about your response too.

I was just thinking if my email address/domain had possibly been blacklisted but that wouldn't make sense either.

There are some email providers that seem to block certain message. It certainly isn't the first time I've seen that happen.

If possible, I'd say try a different email from a different provider to see if that makes a difference. I've found that Yahoo and AOL email addresses are horrible when it comes to blocking important messages and a lot of ISP-specific addresses are too.

Wesley Branton said

There are some email providers that seem to block certain message. It certainly isn't the first time I've seen that happen. If possible, I'd say try a different email from a different provider to see if that makes a difference. I've found that Yahoo and AOL email addresses are horrible when it comes to blocking important messages and a lot of ISP-specific addresses are too.

Sorry about the late response.

I managed to add a secondary email address just now because it no-longer said 'Your email was just returned' after entering the address - like it has been the past few days - and said it had sent a verification email. I followed the link in the email and it threw up the 'same' error below. Despite throwing up that error, it had successfully added the secondary email address and I was able to make it the primary address. I removed my original email address and tried to re-add it but it threw up the same error.

Although the problem is now fixed and it's an inconvenience not being able to use the email address I use for everything else, it does seem very bizarre that this 'email just returned' issue has only just arrised now when I had this email attached to my sync account without issue for a long time.

Anyway, your time was appreciated and thanks for your help. :)

I'm experiencing this same issue with my corporate domain. The difference here is that I'm the IT administrator and I can look at my spam filter where I don't see the message hitting our equipment, and, Office 365 doesn't show the Mozilla message hitting message trace at all.

This is occurring to multiple users in our environment, different email addresses for each, the only unifying element is the email domain is ours.