They look more like server names than "accounts" . Could you post your settings here please? Help /Troubleshooting Information. Clear "include account names" click "Copy text to clipboard", and paste into your next posting here.

When I pasted the entire clipboard I got a message that there was too much so I deleted Important Modified Preferences Thank you

 Application Basics

   Name: Thunderbird
   Version: 38.0.1
   User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1
   Profile Folder: Show Folder

             (Local drive)
   Application Build ID: 20150608103712
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (none) Local Folders, plain, passwordCleartext

   account2:
     INCOMING: account2, , (pop3) mail.comcast.net:995, SSL, passwordCleartext
     OUTGOING: smpt.comcast.net:587, alwaysSTARTTLS, none, true

   account3:
     INCOMING: account3, , (pop3) imap.comcast.net:993, SSL, passwordCleartext
     OUTGOING: smtp.comcast.net:465, SSL, passwordCleartext, true

 Crash Reports

 Extensions

When I send email I get this message- An error occurred while sending mail. The mail server responded: 5.1.0 Authentication required. Please verify that your email address is correct in your account settings and try again. The email shows up in the Local Folders "Sent" folder.

re: Account 2:

    INCOMING: account2, , (pop3) mail.comcast.net:995, SSL, passwordCleartext
    OUTGOING: smpt.comcast.net:587, alwaysSTARTTLS, none, true

The settings for this account are correct, except you have not set the authentication method for outgoing server. So if you try to Send you are likely to get an error message.

Tools > Account Settings > Outgoing server(SMTP) select the server and look at the 'Authentication Method' click on 'Edit' Change 'Authentication Method' to say 'Normal Password'. Click on OK

re :account3:

    INCOMING: account3, , (pop3) imap.comcast.net:993, SSL, passwordCleartext
    OUTGOING: smtp.comcast.net:465, SSL, passwordCleartext, true

The incoming account settings are wrong. This is a POP mail account trying to use imap settings to get mail. This will not work. The outgoing settings should work, but comcast do recommend you use the settings you set in account 2

eg: Outgoing server name: smpt.comcast.net Port: 587 Connection Security: STARTTLS Authentication Method: Normal Password

re :An error occurred while sending mail. The mail server responded: 5.1.0 Authentication required. Please verify that your email address is correct in your account settings and try again.

This sounds like you are actually using account 2 to try to send - hence why you get that error message. Previous comment explains.

Account 3 would not be receiving any mail as the settings for the pop mail account are incorrect.

re: The email shows up in the Local Folders "Sent" folder. This sounds like you have set up account 2 to use a Global Folder and not it's own folders. So, account 2 is using 'Local Folders'. This would also explain why you have only appear to have one mail account showing in the Folder Pane, but were supprised to see two in the Account Settings. I think the mail account you see listed in the Folder Pane may be account 3.

Please confirm which of these accounts is using a Global Inbox.

Tools > Account Settings > Server Settings for the first account (account 2) It should say this at the top. Server Type: Pop mail server Server Name: mail.comcast.net

click on 'Advanced' button What have you got selected? 'Inbox for this server's account' or 'Inbox for a different account' 'Global Inbox(Local Folders)'

If you want it have it's own mail account: choose 'Inbox for this servers account' click on OK

Account 2 is "inbox for a different account Global inbox Local folders" Account 3 is "inbox for this server's account"

All of my email is in Account 2. Can I delete Account 3? I won't change settings until I hear from you.

thank you

Account 3 can be removed assuming it is a duplicate of account 2. Tools > Account Settings select account 3 mail account name ,which is the one with the incorrect server setting. Server Type; POP mail server Server name : imap.comcast.net

click on 'account actions' Select 'Remove Account' Click on OK

Account 2 needs the Authentication method setting as per previous comment.

I deleted account 3. I changed the authentication method for account 2 to Normal Password.

In your earlier message you said "click on 'Advanced' button What have you got selected? 'Inbox for this server's account' or 'Inbox for a different account' 'Global Inbox(Local Folders)' If you want it have it's own mail account: choose 'Inbox for this servers account' click on OK

re inbox, is one option better than the other?

Preference is really a personal thing, both are valid and function perfectly well. The only difference is this: If you use Global Inbox, you will not see a separate mail account and it's own folders in FolderPane.

If you add more POP mail accounts, you have the option to make them use the same Global Inbox as well.

Some people like a less cluttered look of only seeing the one 'Local Folders' account. Others prefer to keep mail accounts separate.

Some info copy pasted from http://kb.mozillazine.org/Global_Inbox Accounts that use the Global Inbox are sometimes called "deferred" accounts.... For deferred accounts, if you go to "Tools > Account Settings > Server Settings" for the account, you will see that "Local directory" does not point to the actual location in your profile folder where the mail is stored. This is normal and necessary because certain files for each deferred account need to be stored separately from the shared mail files. (For instance, each POP3 account has its own file called "popstate.dat" that keeps track of which messages have been downloaded from the server. Account-specific message filters are likewise stored in a separate folder for each account.) If you want to use message aging with a deferred account, note that no settings for the retention policy are provided in the "Disk Space" settings of that account itself. Instead, the retention policy applies where the Global Inbox is located.

You have been very helpful. thanks very much Loel