If you want to remove messages from the server after download, with IMAP, first copy them to Local Folders (can be done with a filter), confirm the copy, then delete from the Inbox (which will delete from the server at the next sync.). Account Settings, Sync. & Storage, Message Sync. is where the choice is made between downloading headers only or full bodies (for offline access).

https://support.mozilla.org/en-US/kb/switch-pop-imap-account

If you switch to POP, remove the IMAP account and add it as POP: outlook.office365.com on 995, SSL/TLS, OAuth2, email address. Delete from server after download is the default setting for POP. But if the account is accessed from several devices, IMAP is the recommended setup.

Thanks for the reply sfhowes. Much appreciated.

From what I have been told here, by GoDaddy support docs and have seen on other sites, it seems it is a requirement to configure new hotmail and similar account setups as IMAP and not POP (GoDaddy email now has to be IMAP for example, even though not "hotmail").

From what I understand and from a small amount of testing, it seems that doing a Move of an email from the inbox to a folder in another email account under Thunderbird results in removing it from that inbox (which will sync back to the Hotmail server and remove it there) but will not affect the email moved to the other account. This is good as my wife and I keep all travel-related email in a travel folder/subfolders in one email account. However, I am of the impression that moving the email to Local Folders and then deleting from the Hotmail inbox will indeed also remove those email from the Hotmail server after syncing, but then moving them back to the local Hotmail TB account will, upon the next syncing, just put them back on the Hotmail server. In essence, it seems to me that IMAP almost renders the local IMAP account setup useless. I mean, why have it local on the PC if it also remains on the server and the PC can just be another device that the email can be accessed via browser?

Regarding stubs vs full email, I found and confirmed the box is checked for full download. Thanks for pointing me in the right direction for that.

Thanks for the reply sfhowes. Much appreciated. From what I have been told here, by GoDaddy support docs and have seen on other sites, it seems it is a requirement to configure new hotmail and similar account setups as IMAP and not POP (GoDaddy email now has to be IMAP for example, even though not "hotmail").

Godaddy has a Microsoft Exchange based mail system that is provided by Microsoft under contract to Godaddy. In all honesty you can compare office365 and the Godaddy offering to some extent. You can not compare Hotmail and Godaddy. I really have no idea what godaddy has to do with this discussion of a hotmail account.

From what I understand and from a small amount of testing, it seems that doing a Move of an email from the inbox to a folder in another email account under Thunderbird results in removing it from that inbox (which will sync back to the Hotmail server and remove it there) but will not affect the email moved to the other account.

That is correct. Once the mail is removed from a folder controlled as a part of the synchronization of content for an account it is effectively deleted from the server (once an IMAP expunge command is issued)

This is good as my wife and I keep all travel-related email in a travel folder/subfolders in one email account. However, I am of the impression that moving the email to Local Folders and then deleting from the Hotmail inbox will indeed also remove those email from the Hotmail server after syncing, but then moving them back to the local Hotmail TB account will, upon the next syncing, just put them back on the Hotmail server. In essence, it seems to me that IMAP almost renders the local IMAP account setup useless. I mean, why have it local on the PC if it also remains on the server and the PC can just be another device that the email can be accessed via browser?

You are deleting the mail from the server and then putting it back when you move the mail back into the IMAP syncronised folder. This is not anything odd, or unexpected. It is a design feature of IMAP. You can remove and add email to a syncronised account.

You can not remove an email from an IMAP account and also have that email listed in the account on Thunderbird. It just does not work that way.

You say the account is a hotmail account. As you can still use POP with a hoptmail account I suggest you add the account to Thunderbird again and select to use POP not IMAP when you do that. It will then be exactly as you have experienced in the past as SFHOWEs suggested.

Hotmail confirm the setting you should use for your account at this link https://outlook.live.com/mail/0/options/mail/accounts although Thunderbird should simply detect the correct settings once you select POP by downloading them from here https://autoconfig.thunderbird.net/v1.1/hotmail.com

Thank you for your detailed reply Matt.

Re GoDaddy and hotmail accounts, my initial problem was with GoDaddy forcing me to shift my email from POP to IMAP. At the same time, we switched ISPs for our home internet. Many years ago, before I knew better, I set up a personal email account with my ISP. Moving now from that ISP for internet, I had to establish new email accounts for my wife and I, which included configuring IMAP. That's where the overlap is. I felt my post was rather long as it was and so I skimped on details but unfortunately that caused some confusion.

Further to my last question, might you know the answer regarding what is the benefit of IMAP for those who have no need to work offline? My wife has no need to work offline. Is there any benefit to leaving her hotmail account as IMAP instead of going POP?

The main benefit with IMAP is the mail is synced between all devices or mail apps, such as phones, tablets etc. If the account is only accessed with one device, POP is adequate, unless you wish to access other folders besides the Inbox, such as the Hotmail Junk folder.