After researching IMAP custom keywords across different email clients and servers, I found the picture isn't entirely clear-cut. Support varies widely depending on your setup, and there's no one-size-fits-all answer.
My research and conversations with #Claude pointed to the same conclusion: custom keywords aren't reliably supported across the board. The recommendation? Stick with folder-based organisation instead, as it works consistently across all IMAP implementations and email services.
That said, I did discover some useful details. Thunderbird handles custom keywords reasonably well. It lets you tag emails with keywords in IMAP folders and will sync those tags to the server if your mail server supports it. If your server doesn't cooperate, Thunderbird stores the tags locally anyway, though other clients won't see them. #email