'  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*                          # optional leading comment
(?:    (?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom
|
" (?:                      # opening quote...
[^\\\x80-\xff\n\015"]                #   Anything except backslash and quote
|                     #    or
\\ [^\x80-\xff]           #   Escaped something (something != CR)
)* "  # closing quote
)                    # initial word
(?:  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  \.  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*   (?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom
|
" (?:                      # opening quote...
[^\\\x80-\xff\n\015"]        itial subdomain
(?:                                  #
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  \.                        # if led by a period...
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*   (?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom
|   \[                         # [
(?: [^\\\x80-\xff\n\015\[\]] |  \\ [^\x80-\xff]  )*    #    stuff
\]                        #           ]
)                     #   ...further okay
)*
(?:  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  ,  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ial subdomain
(?:                                  #
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  \.                        # if led by a period...
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*   (?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom
|   \[                         # [
(?: [^\\\x80-\xff\n\015\[\]] |  \\ [^\x80-\xff]  )*    #    stuff
\]                        #           ]
)                     #   ...further okay
)*
)* # further okay, if led by comma
:                                # closing colon
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  )? #       optional route
(?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom
|
" (?:                      # opening quote...
[^\\\x80-\xff\n\015"]                #   Anything except backslash and quote
|                     #    or
\\ [^\x80-\xff]           #   Escaped something (something != CR)
)* "  # closing quote
)                    # initial word
(?:  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  \.  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*   (?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atfm
|
" (?:                      # opening quote...
[^\\\x80-\xff\n\015"]                #   Anything except backslash and quote
|                     #    or
\\ [^\x80-\xff]           #   Escaped something (something != CR)
)* "  # closing quote
)  )* # further okay, if led by a period
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  @  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*    (?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom
|   \[                         # [
(?: [^\\\x80-\xff\n\015\[\]] |  \\ [^\x80-\xff]  )*    #    stuff
\]                        #           ]
)                           # initial subdomain
(?:                                  #
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  \.                        # if led by a period...
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*   (?:
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...
(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom
|   \[                         # [
(?: [^\\\x80-\xff\n\015\[\]] |  \\ [^\x80-\xff]  )*    #    stuff
\]                        #           ]
)                     #   ...further okay
)*
#       address spec
(?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*  > #                  trailing >
# name and address
)  (?: [\040\t] |  \(
(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*
\)  )*                       # optional trailing comment

<user@dom.ain>