I was migrating from Eudora in 2009, and started using Postbox for Mac — I've been through many versions. In the past, I've used Apple Mail, Thunderbird, and other clients going way back to when I started using email in the 1980s on ARPANET, BITNET. I use Postbox for IMAP and POP mail, and most of my problems have been with the IMAP side.
For some time, Postbox provided support — and would give workarounds for some of the bugs in the software. And there were many! Features promised, like import of Eudora files, simply didn't work — or were only partially implemented, implemented in Beta form only, worked sometimes, were buggy, corrupted files, etc.
Now, Postbox provides NO SUPPORT — I surmise it was too expensive to help clients recover from Postbox bugs, as there were too many. Now there are new releases for majority bugs, but some ongoing issues appear too difficult for them to address. If you file a bug report, it is stored away for their surveys — *you* are simply providing *them* with commercial-value debug support for free.
I have lost enormous amounts of time to Postbox, in corruption of files, and in assisting their tech people to find bugs. Problems are not of one kind, they are over quite a range of features and (non) functions. The latest for me is one in which the ARCHIVE function works several times in succession, and then fails: it DELETES the files, but DOES NOT COPY to the archive, putting in (no subject) vanilla entries instead.
This is NOT power-user software: power users will NOT tolerate this level of bugginess in a released commercial product. When using Postbox, it's essential that you have regular backups, to restore from when the client goes wrong — as it will.
I'd very much like to know what others have found that works better. Considering the reliability rate needed for professional productivity, I find this to be a seriously defective product.