I hope that the bug will be fixed soon. Thanks for the notification!
Though I didn’t have any problems with receiving e-mails from Postcrossing, I’ve still changed the e-mail address just to be on the safe side.
Looking forward to getting good - fingers crossed - news on the issue, and hence having a chance to have my old e-mail back.
We are starting to see some emails to gmx.de/web.de to go through — keep your fingers crossed as we have 4000 queued emails waiting.
One came through to me right now! 
Yay, just got one
If I understand correctly, it is not only that the emails fall into the spam folder, but also that they are not accepted in principle and simply do not reach
Yippieh, my drawn addresses of this morning have just come through! 
@Beatitudinem That’s correct — most emails have not been accepted at all.
In the case of mail.ru, they have been refusing our emails (saying they are spam) with a permanent error code to discard the message and not try again. We have temporarily overridden this (for the main website) so that the emails remain in queue, but some (from yesterday) may have been lost. We have not heard from mail.ru to any of our contacts yet.
Just now I received one from today and some messages via forum. I didn’t realize that this was also mad.
The registration message that I did not get earlier today has just arrived!
Update:
gmx.de/web.de has been accepting emails for several minutes now, so things seems to have been fixed 
— now it should be a matter of the queued emails to slowly get their way through over the next few hours. I don’t expect any emails to gmx.de/web.de to have been lost, but can’t guarantee it.
mail.ru — still no changes. Most emails continue to be refused with a message that they are spam. We can’t even reply to the members who contact us about the email problems as our replies get refused too. We have contacted them multiple times, but are still waiting. If you are a client, insist with them. Emails to mail.ru (& bk.ru, inbox.ru, etc) are currently being queued, but some from yesterday may have been lost.
A registration message from yesterday 21:40 p.m. arrived!
GMX is pretty famous for such issues. Same as web.de (same company). I use GMX and I don´t receive any postcrossing mails at the moment, looks like.
I received some Emails today! One Hurray Message came and emails from the forum that were not from today but from the 10th or 11th March.
I have web.de mail 
I am happy that I received the Hurray Mail!!
Have you read their technical support page? This page lists possible reasons why emails may be considered spam and rejected, as well as possible solutions to the problem.
Unfortunately, we are unable to contact customer support ourselves mail.ru because they are only willing to communicate with email senders. They want the sender to fix all possible issues on own side first. And it will be a “broken phone” if we write to them and then send you messages from support mail.ru and back again
Hi everybody
I sent a separate message to web.de and have just received their reply that things are sorted. Now my missing mails start getting through again.
Barbara
We have, multiple times, but no luck. Even manually typed emails from us (not automated from the website) get refused when sent to @mail.ru — only a tiny amount goes through for some random reason. We already do all the email best practices — something else is amiss on their side.
I suspect something in the spam world happened in the last 24h causing big email providers to over-block. Hopefully they will get a hold of it soon.
The Problem is solved 
Mails that were due yesterday start coming through at gmx. Thank you so much for your efforts, POSTCROSSING admins
Same with web.de
The problem seems to be solved!
Just in case, now I written to the support of mail.ru, but it is unlikely that this will help much, and I think that they will respond to you sooner than to me