Many people converted to use GMail as their primary mail client. I, however, having been used to KMail have found many GMail shortcomings. As a result, I'm still using KMail as my primary email client and try to avoid GMail as much as possible.
Here is what I find problematic in GMail:
- It doesn't work properly in Konqueror. I have to use Firefox to use it.
- It doesn't have a way to filter based on mailing list headers (such as "List-Id", "List-Post", etc.). Thus, often when mail is sent from a mailing list, it still arrives at the inbox.
- It's very hard to follow threads there. They are all on one page.
- The labels list (which double serve as folders) is flat and not a tree.
- It doesn't have KMail's Right-click-on-an-email-address+"Reply to..." feature, which is very safe and convenient.
- Furthermore, when the "Reply-To:" header is set, both "Reply" and "Reply-to-all" do the same thing.
- GMail has no "Send Again" feature to re-send a message that was already sent.
- There is no way to label or delete individual messages - only entire threads. As such, if you purge a mailing list archive you also lose all the mail you sent there.
- Changing the subject line of a replied-to message starts a new thread, not only in the user's GMail account, but for every recipient of the message.
- The GMail editor has a tendency not to put the quoting symbols (">") in the first line of a block.
- GMail disables the forward button in Mozilla. So if you press "Back" you cannot press forward again to go back there.
- GMail has no option to avoid adding the dash-dash-space prefix to the signature. It adds it automatically, without asking. Granted - it can be deleted, and KMail has the same problem too, even for signatures generated by a command line.
- There is no way to select all the unread messages in a label, or all the unread messages across labels.
- There is no indication that an email that was sent actually arrived at a mailing list (to which one is subscribed) after it arrived there.
GMail is not all bad. The search is very fast, which is a joy. But I still much prefer KMail, and refrain from using GMail as much as I can. Perhaps Google can fix most of these problems if they are motivated enough to do so, but from my general impression with the gmail.com QA, they don't seem to care at all.