Hello there info13520.. The reason that you cant receive is corruption in processing files within thunderbird. Try to rebuild the global database. Or the security software is blocking activities to recieve. You already checked these synchronisation options , oke. 1.deleting the ''global-messages-db.sqlite'' files are good to do for reindexing your emails. Close Thunderbird Open thunderbird profile map on that pc. Search for : ''global-messages-db.sqlite '' and remove / delete it. Restart Thunderbird . The program is reindexing the files ,It might take a while . 2. For the security software on that pc try to disable and re-enable that security and anti virus software. It means to do that same disabling and enabling also for the firewalls. And check the inbox for better connection now or take a test mail to that inbox. Leave it disabled for a while. Does it work again , then make that exception in the security software for Thunderbird. 3. To solve and configure this issue further is to check for outdated add-ons you can with our ''troubleshoot mode ''start these tools and configure for outdated or broken add-ons that can disturb the process. https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird 4. Situations can be there that normal internet and the communication to the Thunderbird software that Is blocked by the normal communication somehow between them , you might check. 5. Check for updates for Thunderbird or if this issue is still there after these fixes it can be a server sided problem or port issue try to change the old port number into to other numbers instead port 25 change that port number into 587.Take the latest release from us https://www.thunderbird.net/en-US/thunderbird/all/ if the Thunderbird versions are old. 6. Using these deleting option s for the msf.files from the program if thunderbird is closed l go from there and i do go on to that profile map> Imap map >or mail map ,it is good for the not readable inbox emails to delete these msf.files and then they bring back these normal inbox function s again by starting up thunderbird to see inbox. Both the use of deleting the 'global-messages-db.sqlite files are oke to use and the other methods of deleting msf.files are there to get used to ,i think that deleting 'global-messages-db.sqlite is almost just as good as deleting these msf.file at this disturbing moment but let s stay at the first solving fix first before using everything and mix up all of it. If other ways didn't t help you to go that far to solve it go for a new reinstallation of these Thunderbird accounts. If you think it might be good to solve it with these above explanations, that sounds good and do it. 7. Telephone software does use other protocols and security certifications that are lighter than on the desktop environment. All three providers are having the same issue. It s good to check the antivirus software if it had a new update settings can be changed after that update.disable the connection with that antivirus software as mentioned above in the text to see if thunderbird needs that exception from it. Smtp settings for thunderbird has to be good and be sure of using for each account that email adres at the smtp server settings before sending the new emails for those 3 providers one at a time. And your security and provider protocols has to get checked and likes to have up to date configuration.(ssl/tls). https://support.mozilla.org/en-US/kb/cannot-send-messages https://support.mozilla.org/en-US/kb/cannot-receive-messages