Your most common are likely to be:
- Full stop at end of address
- Commas instead of full stops
- Semi-colon or apostrophe instead of @
- Spaces in middle or at end of address
- Bracketed note in field – eg. (office)
- Double periods
Some common misspellings:
- Googlemail – Gogglemail, googlmail, goglemail
- Hotmail – Hotmial, Hotmal, Hoitmail, Homail, Hotrmail, Hotmil, Hotmaill
- Ntlworld - Ntlwolrd, ntlword, ntl.world, ntlwrold
- Tiscali - Tiscale, tiscalli, Tiscally, Tiscaly
- Btinternet – Btinterent, btinternt
- Yahoo – Yaho, Uahoo, ayhoo
Source: Typical Typos in Email Addresses
Based on the above information, having a list of common email providers which can check after the @ and before the .com would be a nice feature.
Some other typos I could think of (which I do very often) would be typos in .com, so I would normally type .co or .com, so checking these would be useful as well. There is a nice library which I have linked to below which actually does this for you, so take a look.
In terms of the first part of the email address there may be some of the users personal information in there for example, firstname.lastname@example.org, I could misspell this as email@example.com. Although this might be overkill, still worth thinking about.