Mail rejects correct Keychain password data

Question

Intermittent problem Number Three with Mail since Leopard 10.5.x: Mail reports that the server rejects log-in data from Keychain (or possibly ignores existing Keychain data).
I've got Mail checking three mail accounts: Two on the same (POP) mail server, and one Gmail (IMAP) account. Sometimes, when checking these accounts, I get an alert that the log-in data were rejected by the server, and am asked to re-enter the data.
If I re-enter the data, it usually just fails repeatedly; the only solution is to cancel the log-in attempt, take the account offline, then back online and check the mail manually. Subsequent automatic log-in attempts are usually successful; unless they fail.
This happens most often with the first of the three accounts, though it's been known to happen with all three.
I have read advice to others with similar problems which points to a corrupted Keychain. This is quite possible, though I've run Keychain diagnostics which return no errors.
This problem began quite some time ago on my Powerbook G4, and has persisted as I migrated my mail data to my new MacBook Pro.
If anyone has any suggestions or insight, I would be interested.

Answer 1

Open Mac Mail then Command ,  (comma) to open Mail Preferences.
Select the Accounts tab then the Account Information tab.
Type in the correct password under Incoming Mail Server.
Try your email account.
If that didn't help, open Keychain Access located in HD > Applications > Utiliites
Select Passwords on the left.
Use the search field top right corner of the window to locate your email keychain then control click the keychain then click Delete.
Go back to the Mail Account Information window and re type the password under:  Incoming Mail Server.
You should be prompted to save that data to a new keychain.