Text expanders (a.k.a., on your phone: "keyboard shortcuts" in iOS and "personal dictionary" in Android) are great timesavers: Tap a few keys, and instantly whole words or phrases are entered. Here's a very efficient shortcut if you have multiple email addresses:
Use @@ as the shortcut for your main email address and add another @ symbol for each additional address. (For example, @@ = firstname.lastname@example.org and @@@ = email@example.com). When you have to type in one of your many email addresses, it's just a matter of tapping @ to quickly cycle through them and get to the one you need.
At least, that's on iOS. I tried this on Android, but it didn't work with the @ symbol. However, it did work when I used "qq" or "qqq" as the shortcut. The concept is the same, though: You're unlikely to ever type in "qqq" otherwise, and when it comes to entering one of many multiple email addresses, all you have to do is tap the same letter a few times.
You can see the email cycling in action on Rocket Ink or just try it out for yourself (in iOS, go to Settings > General > Keyboard and add a new shortcut. In Android, go to Settings > Language & input > Personal dictionary).