I've always used Outlook on PCs (and on the Mac, for a 30 day trial ) quite happily and successfully, until of course I got on the slippery slope of Apple stuff; you know, once you try a little bit, you eventually have to go all in. So, after reading many, many posts and info about an Outlook to Mail transition, I did it. I was a little concerned at first, as I have a decent amount of email among personal and work accounts, relatively speaking: 8 accounts, including one account with about 30k separate emails. I transferred everything over and held my breath... it worked, wonderfully! I took the time to go through a portion of my 30k email account and weeded out a lot, but I'm still only down to about 24K. So eventually I am confident enough in Mail that I go all in, and use it as my primary email tool. This lasts for maybe 2 months. Within the last few weeks though, it has been acting up. For example, even though all my passwords are saved in the keychain, Mail will still ask for passwords, at random times and not consistent with any particular account. Today it may ask for the password to a Gmail account, tomorrow it might be the Comcast account. It has also started sending emails I wrote in account 1 as if they were coming from account 2, e.g., I'm reviewing emails from a Gmail account, I reply to one, and the person I responded to receives the email from my Outlook account. I will check the smpt list at the top of any new email, and it shows as some of the accounts are offline. ??? There are other issues I've been having as well, but none as frequent as the first two. What has got me a bit confused is that Mail worked flawlessly for a while. I never had these issues. I make sure to delete unneeded emails on a regular basis, including from the "sent" folders. Any ideas? Just tired out?