Email format is like : local_part @ domain_part.com
Local_part & domain_part should not begin or end with special characters ( @#&()*,./{}<>^%[]~`!$=\|;:? ) including hyphen (-)
Local_part & domain_part may contain above special characters like (#$%&*- etc) in middle only.
Limit of lengths for local_part is 64 & domain_part is 255 characters respectively.
domain_part must not contain all numbers
Updated 7/27/2018
^(?![.!#$%&'*+/=?^_`{|}~-])(?:[a-zA-Z0-9]|(?:(?:([.])(?!\1)|[!#$%&'*+/=?^_`{|}~-]))(?!@)){1,64}@(?=.{1,255}$)(?!\d+$)[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$
https://regex101.com/r/dxCmEn/1
^ # BOS
(?! [.!#$%&'*+/=?^_`{|}~-] ) # Local does not start with one of these
(?: # Local
[a-zA-Z0-9]
|
# Special chars
# Local does not end with one of these
(?:
# Option 1
(?:
( [.] ) # (1), Not a consecutive special char (specific), add more
(?! \1 ) #
| # or,
[!#$%&'*+/=?^_`{|}~-] # One of these other special chars, remove from here
)
# Option 2
# | ( [.!#$%&'*+/=?^_`{|}~-] ) # (1) Not a consecutive same special char
# (?! \1 )
# Option 3
# | [.!#$%&'*+/=?^_`{|}~-] # Not a consecutive any special char
# (?! [.!#$%&'*+/=?^_`{|}~-] )
# Option 4, Original
# | [.!#$%&'*+/=?^_`{|}~-] # Any special char is OK
#
)
(?! @ )
){1,64} # 1 to 64 local characters
@
(?= .{1,255} $ ) # 1 to 255 domain characters
(?! \d+ $ ) # Domain must not contain all numbers
[a-zA-Z0-9] # Domain
(?:
[a-zA-Z0-9-]{0,61}
[a-zA-Z0-9]
)?
(?:
\.
[a-zA-Z0-9]
(?:
[a-zA-Z0-9-]{0,61}
[a-zA-Z0-9]
)?
)*
$ # EOS
So based on your limited description it seems like you're looking for something like this?
Here is the pattern: ^(?<localpart>[^-].*[^-])@(?<domainpart>[^-].*[^-])\..{2,3}$
It saves them into named capture groups, and it assumes that both the localpart and domainpart contain at least 2 characters (which they should). Neither parts are allowed to begin or end with -.
Are there any other requirements or does this pretty much cover it?
