There are a number of new, useful features in Mac Mail, such as improved searching for attachments and a button to delete an unwanted message from a notification banner. Nice. However, if you are using Mail as a client for one or more Google Gmail accounts, there are new issues, some serious.

Worse, for those who have tweaked Mail or Gmail preferences in the past to account for Gmail's particular message handling, then a blind upgrade to Mavericks may prove problematic.

In a long post at TidBITS, Joe Kissell runs down the issues. The problems for most users will be that Mail takes a significant time to display messages in the Inbox and other mailboxes — here "significant" could be more than a day, even a several days, depending on the number of messages stored. Mail, it appears, is reindexing folders and performing other tasks, but doesn't tell the user. Depending on user's Gmail settings, it could be downloading gigabytes of already read messages.

For longtime Mac power users, AppleScripts written for Gmail accounts will likely be broken with this initial move to Mavericks Mail. Some mailboxes will be reported as empty but have messages in them. Ordinary rules are also having problems, according to some reports.

In addition, Megan Lavey-Heaton at TUAW mentions problems with Smart Folders in Mail after updating.

It kept telling me I had numerous unread messages, but nothing was showing in the mailbox. In the screencap above, you can see the smart mailbox selected but nothing in the mailbox itself. When I checked the rules for that smart mailbox, it had a lot of blank rules that weren't there before. I deleted them, but the smart mailbox still didn't work.

Kissell reports that some Mail users in before the release of Mavericks, would prevent the All Mail label from being exposed to IMAP clients (a setting in Gmail), since having All Mail set could result in having multiple copies of messages downloaded to the client Mac. This was especially a concern with MacBook Airs and other systems with limited bandwidth and constrained SSD "disk" space.

In his TidBITS article, Kissell describes the procedure to undo this past practice of prevent the All Mail label from being exposed and what to expect when turning it back on.

Now, here’s what’s going to happen. Mail — despite the fact that it has already cached all your Gmail messages — will download all of them again. For me, with about 321,000 messages totaling over 4 GB, that took nearly two full days, even with a super-fast Internet connection. That’s an unreasonably long period of time, and a crazy waste of bandwidth since I already had copies of all those messages! Mail actually does this in stages, and I won’t bore you with the details, but I will say that at a certain point in the process, your ~/Library/Mail folder could be twice as large as it should be, or even larger. Unless you’re running critically low on disk space, don’t panic about that, because it’ll eventually settle down — but be aware that it could take Mail a very, very long time to purge all those duplicate messages and return your ~/Library/Mail folder to a reasonable size. When that big download is done, the good news is that Mail will have only one copy of each message — the one in All Mail! Messages you had labeled in Gmail will still show up in mailboxes bearing the same name. (And, for the first time, Mail will have a copy of all your messages that didn’t have any label at all — ones you had archived without explicitly filing.) But those messages are not really in those mailboxes. What Mail does behind the scenes is to add a little invisible XML code to the end of each message telling it which other mailbox(es) it should be displayed in. And that’s an entirely reasonable strategy, as far as it goes. In fact, arguably Mail should have started doing this years ago.

At the same time, there are reports that after all the old messages are downloaded, cached and indexed — again – the Mail’s Inbox won't stay in sync with Gmail’s Inbox. This isn't a new problem and has been reported for several years.

Now, I have seen these delays pop up now and again under Lion and Snow Lion. They aren't so new. For example, at times when I've known a message is coming, I've then discovered the message when checking Gmail in the browser. There it is, on time, but delayed in Mail. Yikes!

If you haven't upgraded yet, good. Wait. If you have upgraded, then make sure to keep Mail open and be patient with the background processes.

There are many things to consider with Mail. For example, the badges for unread messages will be off count, perhaps significantly. It could be greater than actuality.

Meanwhile, I am looking at other Mac email clients. But that's an article(s) for another day(s).