It is correct. The bit you underlined is the name of the 'imap mail account name' folder. If you add more imap gmail accounts, you will find that they get added with an additional number appended. eg: imap.gmail-1.com, imap.gmail-2.com

In Account Settings: The name of your mail account is by default the actual email address, although you can edit it. Personally, I leave it as it is because it is just easier to instantly see what mail account settings I'm viewing. It is displayed in the left Pane. If you select the name in the left pane, the details will be shown on the right side and that includes the email address. Example image below.

The image you posted displays the 'Server Settings' and also the location of Message Storage for that account.

Even if my Accoulnt Name is filled up, the server name still used by default in Local Directory parameter. What is the point to name account directory as imap.gmail-1.com, imap.gmail-2.com, etc? To create clutter and confusion in directories? Wouldn't it be better to use by default an Account Name instead? And actually "Message Strorage" is not the property of a server, so it would be better to place it on another tab.

re :Wouldn't it be better to use by default an Account Name instead? No because account names can be edited. Email addresses are also usually used as UserName setting. This has nothing to do with account names.

re:And actually "Message Strorage" is not the property of a server, All imap accounts store all emails on the server and the imap account synchronises folders with server to show what is on the server, not the other way around. Message storage is shown as it is in the same section that has settings for downloading messages, so it makes sense to know where that downloaded location is in the profile.

In the case of a POP account, old deleted pop accounts can be relocated again by pointing to look in a different location.

re: account names can be edited So what? I just suggested to use account name (or email address) as DEFAULT Local Directory name when creating an account. It is not logical to use server name for account directory. I add an email account, not a server, after all.

The bottom line is this, you do not have a problem, but you wondered why the editable account name is not used. Your email provider provides the mail server(s) that get, store and send messages. Thunderbird uses that mail server name for a mail account folder name which is not the same as an account name.

re: Your email provider provides the mail server(s) that get, store and send messages. Thunderbird uses that mail server name for a mail account folder name

Yes, it is true, but for mailbox server name used along with username, and account corresponds in meaning to e-mail, not the server. And why exactly incoming server name is used? In this directory all folders are stored, and sent messages too! Where is the logic? So I really don't understand why incoming server name was choosen as account main identifier. By the way, server name also can be edited in account, and then, it will not match with account directory name :)

re: you do not have a problem

Well, everything works and from this point of view, there is no problem. Of course, account directory could have any name. Like imap.gmail-13.com. Or a counter. Or a GUID. Unless you have to do something with mail directories. Current default directory name gives absolutely no clue about which exactly account it contains. If you are used to making some kind of backups or file manipulating (as in my case), it could be problematic.

Several days ago I decided to try to migrate from TheBat! to Thunderbird. I have a dozen of POP mailboxes with a long message history at my PC. And many of them was at the same mail servers. I have made an export of messages from each mailbox in UNIX mailbox format. Then, I have added all of my mailboxes as new accounts in Thunderbird. Next, as it was described at forums, I needed to copy these files to corresponding account directories. I have opened Mail directory hoping to find folders corresponding my mailboxes. But I didn't find them. I saw a strange list of directories, looking nothing like my email addresses. The another reason of my confuse was that default directory name is not displayed and cannot be changed before the account is created.

It was a problem to identify my mailboxes, so I had to change directory for each of my account to corresponding to email address. And after every change Thunderbird was restarted.

So I see a usability problem here. And the saddest thing for me is that the community don't want to notice oddities which are OBVIOUS and is not interested in making its product better...

TheBat! forever! :)