I can confirm some of the issues Gizmo is reporting
For the most part, the message avatars work great. I don’t know what source is being used, but they are much, much better than those that Apple Mail uses (which are more contacts book-based).
That being said, I have never experienced the wrong avatar being used for a sender, but I have seen the avatars go (for lack of a better description) from a premium-sourced to looking stock-sourced. For example, an image avatar would be replaced by a letter from time to time.
I “believe” that, based on prior conversations I have had here on this issue, it’s a sync issue or an update process that occurs from time to time.
But again, on the whole, the avatar source that is being used is more universal and robust than what I have seen other email clients like Apple use.
We would need more information about all these issues to be able to address it as we are not able to reproduce them, so original forum links, screenshots, videos, urls, specific email addresses with gravatar issues and so on would help.
This happens to me when one of the senders does not have a photo or avatar at their end. In a conversation, the avatar shown is the avatar of someone who has an avatar or photo at their end. My solution was to add a photo to the person’s entry in my Contact list (Windows). That solved the problem that the avatar photo matches the sender now in a conversation instead of showing the avatar of the next person in the conversation who does have a photo or avatar.
The issue is at the sender’s end however we can’t control whether they use an avatar or photo unless you know them well enough they will let you make adjustments to their email profile.
eM Client’s import feature totally fails to import any of the account-specific folders I used in Postbox to keep and store important email messages. This, alone, is a deal breaker unless there’s a way to transfer the content of those folders manually, and I haven’t yet discovered a way to do that.