^[a-z0-9!#$%&'*+-/=?^_`{}|~]+(\.[a-z0-9!#$%&'*+-/=?^_`{}|~]+)*@[a-z]([-a-z0-9]*[a-z0-9])?(\.[a-z]([-a-z0-9]*[a-z0-9])?)*$
One can most likely do without most of the characters in the local-part.

To use:
$  egrep '^[a-z0-9[a-z0-9%&'\''*+-/=?^_`{}|~]+([.][a-z0-9!#$%&'\''*+-/=?^_`{}|~]+)*@[a-z]([-a-z0-9]*[a-z0-9])?([.][a-z]([-a-z0-9]*[a-z0-9])?)*$'

Extended to allow underscores and leading digits to the domain name:
^[a-z0-9!#$%&'*+-/=?^_`{}|~]+(\.[a-z0-9!#$%&'*+-/=?^_`{}|~]+)*@[a-z0-9]([-a-z0-9_]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9_]*[a-z0-9])?)*$


Some references:

RFC2822 (Internet Message Format)

quoted-string   =       [CFWS]
                        DQUOTE *([FWS] qcontent) [FWS] DQUOTE
                        [CFWS]
text            =       %d1-9 /         ; Characters excluding CR and LF
                        %d11 /
                        %d12 /
                        %d14-127 /
                        obs-text
obs-text        =       *LF *CR *(obs-char *LF *CR)
obs-char        =       %d0-9 / %d11 /          ; %d0-127 except CR and
                        %d12 / %d14-127         ;  LF
obs-utext       =       obs-text
obs-phrase      =       word *(word / "." / CFWS)
obs-phrase-list =       phrase / 1*([phrase] [CFWS] "," [CFWS]) [phrase]
dcontent        =       dtext / quoted-pair
dtext           =       NO-WS-CTL /     ; Non white space controls

                        %d33-90 /       ; The rest of the US-ASCII
                        %d94-126        ;  characters not including "[",
                                        ;  "]", or "\"
atext           =       ALPHA / DIGIT / ; Any character except controls,
                        "!" / "#" /     ;  SP, and specials.
                        "$" / "%" /     ;  Used for atoms
                        "&" / "'" /
                        "*" / "+" /
                        "-" / "/" /
                        "=" / "?" /
                        "^" / "_" /
                        "`" / "{" /
                        "|" / "}" /
                        "~"
atom            =       [CFWS] 1*atext [CFWS]
dot-atom        =       [CFWS] dot-atom-text [CFWS]
dot-atom-text   =       1*atext *("." 1*atext)
phrase          =       1*word / obs-phrase
addr-spec       =       local-part "@" domain
local-part      =       dot-atom / quoted-string / obs-local-part
quoted-string   =       [CFWS]
                        DQUOTE *([FWS] qcontent) [FWS] DQUOTE
                        [CFWS]
qtext           =       NO-WS-CTL /     ; Non white space controls
                        %d33 /          ; The rest of the US-ASCII
                        %d35-91 /       ;  characters not including "\"
                        %d93-126        ;  or the quote character
qcontent        =       qtext / quoted-pair
quoted-pair     =       ("\" text) / obs-qp
obs-qp          =       "\" (%d0-127)
obs-local-part  =       word *("." word)
word            =       atom / quoted-string
domain          =       dot-atom / domain-literal / obs-domain
domain-literal  =       [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS]
obs-domain      =       atom *("." atom)


RFC1035 (DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION).

<domain> ::= <subdomain> | " "
<subdomain> ::= <label> | <subdomain> "." <label>
<label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]
<ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>
<let-dig-hyp> ::= <let-dig> | "-"
<let-dig> ::= <letter> | <digit>
<letter> ::= any one of the 52 alphabetic characters A through Z in
upper case and a through z in lower case
<digit> ::= any one of the ten digits 0 through 9