I've noticed that GitHub (which I assume uses this Markdown parser) doesn't properly process certain email addresses in its autolink feature. Some times it will convert things which aren't email addresses and other times it won't convert things that are. See reference to RFC 3696 and the formatting of valid email addresses.

For example, valid e-mails not parsed (see Babelmark as well):

• a!b@test.com (note the a! is missing)
• "a..b"@test.com (quoted parts are ok)

and invalid e-mails parsed:

• a..b@test.com (can't have consecutive '.')
• a.@test.com & .a@test.com (can't start/end with '.')

These are the full list of valid examples from the RFC (only 2 succeed here):

• Abc@def@example.com
• Fred\ Bloggs@example.com
• Joe.\Blow@example.com
• "Abc@def"@example.com
• "Fred Bloggs"@example.com
• user+mailbox@example.com
• customer/department=shipping@example.com
• $A12345@example.com
• !def!xyz%abc@example.com
• _somename@example.com

And valid from Wikipedia:

• simple@example.com
• very.common@example.com
• disposable.style.email.with+symbol@example.com
• other.email-with-hyphen@example.com
• fully-qualified-domain@example.com
• user.name+tag+sorting@example.com (may go to user.name@example.com inbox depending on mail server)
• x@example.com (one-letter local-part)
• example-indeed@strange-example.com
• admin@mailserver1 (local domain name with no TLD, although ICANN highly discourages dotless email addresses[13])
• example@s.example (see the List of Internet top-level domains)
• " "@example.org (space between the quotes)
• "john..doe"@example.org (quoted double dot)
• mailhost!username@example.org (bangified host route used for uucp mailers)
• user%example.com@example.org (% escaped mail route to user@example.com via example.org)

And some invalid ones from Wikipedia:

• Abc.example.com (no @ character)
• A@b@c@example.com (only one @ is allowed outside quotation marks)
• a"b(c)d,e:f;gi[j\k]l@example.com (none of the special characters in this local-part are allowed outside quotation marks)
• just"not"right@example.com (quoted strings must be dot separated or the only element making up the local-part)
• this is"not\allowed@example.com (spaces, quotes, and backslashes may only exist when within quoted strings and preceded by a backslash)
• this\ still"not\allowed@example.com (even if escaped (preceded by a backslash), spaces, quotes, and backslashes must still be contained by quotes)
• 1234567890123456789012345678901234567890123456789012345678901234+x@example.com (local part is longer than 64 characters)