I was re-thinking about this feature request, because some customers asked us again when it will be available and was asking myself, with the little knowledge I have of how SmarterMail stores the data, how it could be done.
As far as I know flags for mails are stored in mailbox.cfg so that would maybe the place to add support for custom tags.
The problem with custom tags/keywords is that they are in fact custom so it would not be suitable to add a column in the cfg for each of them. Well There are some consensus about the name of certain tags but still.
Could a solution be to add a single column in mailbox.cfg, like for example imaptags, and store them as a json object in that column (as long as mailbox.cfg supports dynamically sized text fields?).
Then any imap client could store whatever tags it wants for a mail and that would be stored like this.
Could this makes sense ?
That would be the first step and then add then support for it on the imap service.
Next step which could be a plus would be to add support for some common custom tags in the webmail for example to colorize/categorize some mails, but the most important is to have at least the tags saved so they are reported between imap clients.