Hmm, the password does conform, but is not the original one. I must have changed it sometime in the last five years. A few years ago Apple informed me that if my name was Eric Jervis I lived in Stoke on Trent. There is AN Eric Jervis in Stoke but that is not me. I dimly remember we sorted it out on the phone.
You could try logging in to iCloud.com on your Mac. This will ask for your user name and password but also offer you a "Forgot Password?" option so you can reset it. However, if you do, you'll need to update it in Mail if you use an iCloud email address - and don't forget to change it on your written password sheet (wink emoji!)
I have my fingers firmly crossed because I might just have found the cause of Mail crashing repeatedly (and I mean repeatedly). This was happening with no discernible cause - moving to another mailbox, mid-way through writing an email, or even when just reading an email. I tried starting in Safe mode and Mail crashed more or less immediately.
One solution suggested was to remove the Mail preference files and then restart, when new files would be created. Did that and was horrified to see that all my saved mails had disppeared, so I hauled a previous version of Mail from Time Machine and got them back. The last resort was to follow a suggestion to find and remove a faulty email. I have literally hundreds of mails in various folders. So I put this idea off until today and then created a Desktop folder for storing the emails. I tried moving mailbox folders across from Mail but found that you can't do that. So I created a sub-folder in the Desktop folder and then moved the contents of the matching mailbox folder one-by-one.
So far, so very good. I have spent a jolly 10 minutes clicking through the dozens of folders in Mail to try to provoke a crash, but nothing happened. Yet. You will hear me scream if mail crashes again!
Eric Jervis 