re :'No Junk' button, and I can see that the mail is moved to the inbox: The inbox label changes to bold (1) to indicate a new unread message.

Thinking out aloud here... When email is moved to Inbox and marked as 'unread', it is possible that the server spam filter, the Thunderbird junk filter and also any other filters on server or in Thunderbird will run again on the 'new unread' message.

Please provide some additional info.

1. Do you know which filter put the email was in the server 'Spam' folder in the first place? Did the server spam filter put it in the Spam folder? Did Thunderbird junk controls put it in the imap 'Spam' folder?

2. Menu icon > Activity Manager Does it mention anything about moving message from 'Spam' to 'Inbox' ? Does it mention anything about deleting that message from Inbox shortly after moving it ?

3. Do you have any Thunderbird Message Filters set to delete emails? If yes, check the filter conditions to see if they could have deleted that email.

4. Is the email address of sender in one of your address books? If yes, have you set up your Thunderbird Junk Controls to recognise that address book as a whitelist?

5. In Thunderbird Account Settings > Junk Settings for the mail account, have you selected the checkbox for Thunderbird to trust eg: Spamassassin?

6. What OS do you use? What version of Thunderbird? What server are you using eg: gmail ?

Also... How old was the email which marked as junk ? Could it have been auto deleted by server or Thunderbird based on age ? Some servers auto empty junk after X days.

I'm thinking out aloud here again, so if I'm barking up the wrong tree, I'm ok with being corrected.... if the email had been deleted by server due to an auto deletion based on eg: age of email, but server as yet had not synched with Thunderbird imap 'Spam' folder, email would still looked available in Thunderbird. Then, when email was moved to imap 'Inbox' in Thunderbird, the imap Inbox and imap Spam would have synched with server, but as email had already been deleted off server, the newly synchronised Thunderbird imap Inbox could not show the email.

Thanks for your interest. My answers: First to the second post: That are always new mails. I usually see them some minutes after arriving, and then try to declare them "No Junk". Now first post 1. There is only Thunderbird's self learning junk filter. I do not use Thunderbird's third party filters like SpamAssasin. I deactivated spam filtering at my provider . 2. German message meaning "from spam moved to inbox". No deletion log. 3. None of my filters deletes mails. 4. Not in my address list. 5. No check box set (see 1.). 6. I have Windows 7 Sp1 64bit, Thunderbird 60.5.0 321. bit. Provider is 1und1 (now IONOS). Server type IMAP.

Peter

BTW: I'm researching this behaviour since several weeks w/o success, and this post was my "final trial". My thoughts are very similar with your "loud thinkings".

I found the way how this misfunction appears. It is not on TB side, it is a "feature" of the SMTP server, maybe only of SMTP.IONOS.DE.

There exist two mail adresses, for example first@ionos.de and second@ionos.de

While first has a post box, second is only redirected to first.

Mails in TB's spam folder therefore have one of the adresses in the TO field of their header.

When a mail is declared as Not Junk, it is moved to the TB's inbox. Inbox tells IMAP about a new message.

That is okay with the address first@ionos.de, everything runs at usual. But on a mail for second@ionos.de IMAP recognises, that the mail must not be stored in the inbox. It marks the mail as "To be deleted" (those mails are periodically really deleted from the server), and tells TB that the mail is deleted. Then TB deletes the mail, w/o sending it to trash.

In spite it is not a bug of thunderbird, maybe there are suggestions for a workaround?

re: While first has a post box, second is only redirected to first. Is the second email address redirected via servers ? In other words the second email address webmail is redirected to first webmail account and then both email addresses are downloaded to Thunderbird first email address account?

Assuming you have one email address/mail account and emails are redirected from server to server. Try putting the second email address as an identity of the first email address.

In Thunderbird

• right click on mail account name in Folder Pane and select 'Settings'
• Click on 'Manage Identities' button
• click on 'Add' button
• add all details of the second email address.
• clickon 'close'
• click on 'OK'

Good info on 'Identities' at this link. This sounds like the solution you may be looking for.

• https://support.mozilla.org/en-US/kb/using-identities

Great! Many thanks. In addition to the TB change I only have to remove the redirection at my server.