I presume this is an IMAP account, in which case Thunderbird is just coping with internet traffic. Your internet connection is the issue here.

It can't be an internet problem. After this problem cropped up, I upgraded our Spectrum internet to 1 gig, and upgraded to a WiFi 7 Orbi system. This Thunderbird delay still persists. That said, the delay wasn't occurring with the old router and 500 meg network, back in January.

This cropped up after a Thunderbird upgrade - perhaps in January 2026.

Several possible issues.

Disable ipV6 on your router and local system network interfaces and perhaps also in Thunderbird.. that sort of stuttering is a sign it is not working well and after failure falls back to IPV4

Interent speeds from providers are usually described in terms of download speeds, not uploads. Commercial services are usually symmetric, domestic only the uploads (which IMAP uses extensively) are usually in the order of 1/10 of the download speed. I notice Spectrum appear to not publish upload speeds.

I guess thatdidn't understand the meaning of the first answer to my query about this problem. I am NOT trying to move or copy email to an external internet server. In each case, I am simply trying to move individual emails to a folder on m own LOCAL HARDDRIVE / SSD.

Given this information, is it possible that I have uncovered a flaw in a recent Thunderbird update?

Thank you for your continued attention !

Are you using IMAP? If the answer is yes then everything involves a round trip to the server, even saving the email as an external EML file.

As you do not actually say what protocols you are using I have to guess that it is the default. And the server will not affect you antivirus slowing things down. They are just as adapt at standing in the way when updating local files as they can be with internet connected actions. Sometimes worse with local things because Windows is a terrible housekeeper so the writing of things to the system temp folder can take an age. Many Thunderbird users never compact their folders either, so when a email is marked read a multi gigbyte file is scanned for the 20th time today and perhaps even more than once in the last minute. Fast hardware does not always cover repetitive and pointless activities like scanning on the receipt of each and every email and again each time is it moves (two locations change so two files) or changes state (marked as read is enough to see the file updated and another scan kick off. so they just get bigger with every email that is moved or deleted.

There is a reason I use Windows defender, it does not do that. Almost all paid antivirus products need significant modifications to make them work well with Thunderbird because they assume we all browse the web exclusively and file are small. Mail files have not been small for 20 years.

According to my Server Settings in Thunderbird, I am using a POP mail server. This delay in the Move process has never occurred prior to two-to-three months ago, and I have been using Thunderbird for at least twenty years. I suppose Windows 11 could be interfering with this Move process, but it seems to be much more likely that a recent software change in Thunderbird has caused this problem. PLEASE look into it. Thank you for your time.

Something is interfering with thundebird, possibly an VPN or anti-virus. I have seen no other posts about slowness of POP accounts,