migration of email account settings to new macbook

I am retiring my late 2013 MB Pro (BigSur version 11.7.10)and switching to the new M4 MacBook Air.

Migration did not work, told me I didnt have neough disk space despite the discs both being 1Tb.

But that aside i am manually adding my 4 email accounts to mail accounts - or trying to.

I have tried hovering over passwords in account settings, keychain access, guessing them lol but nothing works and I cant find any reference to them in keychain apart from old entries with passwords that no longer work.

If anyone has any ideas or guidance - for example what is the description for an email passowrd acc in the keychain, is it something like 'oauth' for example??

Literally hundreds of entries in thje keychain and no idea what to search for/look for..

Pretty pi_s_d with it all to be honest....

Regards

Mark