This is the possible first in a series of posts on Gmail’s idiosyncratic behaviors with Mail on Macs, iPhones and iPads.

Many of our clients who interact exclusively with their Gmail or Google Apps accounts through their Macs and iPhones have reported messages “disappearing”.

Here’s what’s usually happening: by default, when you add a Gmail account to an iPhone or iPad, there’s an option to “Archive” messages rather than put them in the trash, and it’s enabled by default, which you’d never know because iOS doesn’t show it to you unless you go back and look at the account settings after you add it.

There’s also a general Mail option to Ask Before Deleting, which is off by default.

What this means is that when you’re looking at a message, there’s an “archive” icon at the bottom of your screen where the trash usually is. And if you simply tap it once, which is easy to do unintentionally, the message vanishes from whatever folder you’re looking at it in, without any confirmation.

The message hasn’t been deleted. It’s instead in the Gmail “All Mail” folder, along with every single message that you send or receive, regardless of what other folders they may (or may not) appear to be in. “All Mail” sort of makes sense when you’re on Gmail in a web browser, and you work with labels applied to messages, rather than messages within folders.

However, “All Mail” is confusing in Mail a Mac or an iPhone, and its presence causes duplicate copies of everything to be downloaded. So we usually have it NOT appear on a Mac or an iPhone. But, if you then tap the archive message button an an iPhone or iPad, the message really does seem to have completely vanished.

So what we recommend is:

• In Gmail or Google Apps on the web, go to Settings -> Labels, and in the “System Labels” section, ensure that only Sent, Trash, Drafts and Spam have the “Show in IMAP” checkbox set.
• On all iOS devices you may have, go into Settings -> Mail, Contacts, Calendars and set Ask Before Deleting to on. This will require confirmation before you archive, as well as give you the option of moving the message to your Trash instead, for each message.
• If you need to find an archived message, log into Gmail/Google Apps on the web and look in your All Mail folder.
• If you have no need for archiving, where a message is hidden from view but is never really deleted, you can go to Settings -> Mail, Contacts, Calendars -> your Gmail account and turn Archive Messages Off. This will restore the Trash can icon.

Also, just to add to the confusion: OS X Mail also has an Archive function, but it behaves completely differently than iOS with a Gmail account. OS X Mail will create a folder called “Archive” and move the message you’re looking at there.