I’d like to move my character Nombeko-Earthshaker to Firemaw, but transfer cannot be done.
"Error. Please address these issues:
Mailbox is empty, I haven’t played this character in very long time.
Hey Gorgothra,
Sorry to hear that this invisible mail is preventing your transfer. Please do open a ticket if the issue persists, and a game master should be able to help you as soon as possible. 
Thanks for reply.
I don’t know how to open ticket and send it to actual GM. Everything I have tried just redirects me to some know issues. The whole UI of customer support is perplexing and overwhelming.
I have the same problem.
Things I’ve tried:
I’ve sent a ticket in. It was extremely difficult to reach the actual ticket sending, the AI kept redirecting me to useless “solution propositions”.
GM gave me two solutions to attempt, neither worked, third option was to report bug to forums. So I’m reporting it here.
My main character is now stuck in Earthshaker 
For almost four days now I have been trying to use the free character transfer Service to transfer my character “Owlgobrr” from Mograine-EU to Gehennas-EU.
Every time I get the same error:
Error. Please address these issues: - Please clear the mail from this character’s mailbox.
I check my mailbox every few hours but no new mail arrives in my inbox. I thought eventually some npc mail will arrive but nothing happened.
When I opened a support ticket all I got was instructions on how to remove addons and reset the game to default configurations.
If that didn’t work I was told to open a thread on the support forums to resolve the issue.
(I think the existence of this thread proves it wasn’t solved by disableing addons and resetting configurations)
I am grateful for your help in resolving the issue.
I am having the same issue.
I have no one blocked or ignored, no mail, not quested or even logged on in the last month.
I have same issue, I can’t even find how to write a proper ticket to actual human being. Everything redirects me to some sort of “know-how”.
Reporting that I have the same issue. I posted repro steps in another thread with the same problem. Earthshaker to Firemaw transfer.
(Can't transfer character, buggy mail in mailbox - #4 by Elíanora-earthshaker)
This has been an extremely frustrating experience. It keeps redirecting you to some dumb “attempt this” generated by AI and doesn’t allow you to proceed to start a ticket. 
Try this
https://eu.battle.net/support/en/help/contact/464/ticket
Always look for the still need help button at the bottom and then contact support. I know support is a pain to navigate to make tickets, it’s done on purpose to weed out issues that can already be resolved.
Hello there! Same problem with that character on Earthshaker. I have ckecked and tried everithing, still error “Please Clear the Mail from this Character’s Mailbox”. May be because of brewfest subscription, but I can cancell it on in September. So, obviously, only GM able to solve that issue, there is simply no button “delete hidden mails”. Another fun thing is that you have to wait 6 days for your ticket response, quite poor support quality.
Update:
I’ve managed to contact GM, they don’t have a workaround or resolution to help us with an invisible mails yet.
I don’t know but everything about World of Warcraft feels terrible and dissapointing.
I have tried everything in the article and buying from ah to try to reset the mail system. Still stuck with "“Please Clear the Mail from this Character’s Mailbox”.
This is way past stupid at this point.
Hey Gorgothra,
Could you try again to transfer your Shaman please?
Got same issue at the moment, the ticket wait time says 6 days 20 hours.
The ticket had to be re-opened as it was closed with auto - replay “Try this, read this etc.”
I’m just thinking - Maybe writing here would help speed up the process.
Thanks in advance
Fuzzx - Golemagg
Also having this issue, also on Earthshaker. Not played in months so it’s not NPC/quest mail, cleared brewfest & currency conversion mail.
Hello!
I would like to transfer my character Marrish-Gehennas to Firemaw, but i’m currently getting: “please clear the mail from this characters mailbox”.
There is 3 days since I faction changed. I got a brewfest mail after 24h ish and all the cata pre patch mails. I have tried to buy something from the auction house and still nothing works. I have tried everything in the article as well.
Same issue as everybody else here.
2 of my characters on Mograine-EU (Philerino, lvl 80 shaman and Malphina, lvl 79 death knight fwiw) are stuck there due to mailbox issues, every other character I already moved to Gehennas (9 characters iirc) had no issue transferring immediately.
The 2 stuck characters are the only 2 characters I have that are part of the Brew of the Month club. So it appears that’s the primary issue. And yes, I already drank May’s brew (Springtime stout fwiw) on both characters, their mailboxes are empty and have been empty for 3 days now, as far as visuals go.
This has been a known issue for over a year now, how come there are no work - arounds?
Like unstuck button, theoretically it could be possible to add a button - Delete all mail (including invisible mail)
That’s if you have a US account (or you can report it in the US bug forum if you have a character over L10 in the US. In the EU the bug report tool is ingame.