How to extend a macro for e-mail addresses to support multiple arguments?

Question

I prepared the following macros to format e-mail adresses in a e-mail header.

\usepackage{xifthen}% Provides \ifthenelse and \isempty

% E-Mail header strings with format.
\newcommand{\fromString}{\textbf{From:} }
\newcommand{\toString}{\textbf{To:} }

% E-Mail with or without alias.
\newcommand{\email}[2][]{%
    \ifthenelse{\isempty{#1}}%
        {<#2>}% E-Mail only
    {"#1" <#2>}% Alias and E-Mail
}

% E-Mail header From:    
\newcommand{\emailFrom}[2][]{%
    \ifthenelse{\isempty{#1}}%
        {\fromString \email{#2}\\}% E-Mail only
    {\fromString \email[#1]{#2}\\}% Alias and E-Mail
}

% E-Mail header To:
\newcommand{\emailTo}[2][]{%
    \ifthenelse{\isempty{#1}}%
        {\toString \email{#2}\\}% E-Mail only
    {\toString \email[#1]{#2}\\}% Alias and E-Mail
}

The macros can be used as illustrated by the following examples. Please mind that [] are used for optional arguments instead of {}.

\email[Doe, John]{john.doe@stackexchange.com}
\emailFrom[Doe, John]{john.doe@stackexchange.com}
\emailFrom{john.doe@stackexchange.com}
\emailTo[Doe, John]{john.doe@stackexchange.com}
\emailTo{john.doe@stackexchange.com}

The formatted output looks like this:

"Doe, John" <john.doe@stackexchange.com>
From: "Doe, John" <john.doe@stackexchange.com>
From: <john.doe@stackexchange.com>
To: "Doe, John" <john.doe@stackexchange.com>
To: <john.doe@stackexchange.com>

How could I extend the macro so that I can use it with multiple e-mail addresses? The following example should explain the issue. As you can see by the third example, the occurance of the alias is individual for each e-mail entry.

To: "Doe, John" <john.doe@stackexchange.com>, "Doe, Jane" <jane.doe@stackexchange.com>
To: <john.doe@stackexchange.com>, <jane.doe@stackexchange.com>
To: <john.doe@stackexchange.com>, "Doe, Jane" <jane.doe@stackexchange.com>

Since I am new to using macros in latex you are also welcome to generally improve my commands or leave comments to do so.

---

Update:

While working with several email I realized that it can also happen, that there is no email address given, only the email alias. This happens when someone forwards emails e.g., as an internal conversation in a company. Nevertheless, I accept this format as a valid email header. Do you see any chance to include this schema in the macros? Here is an example.

From: John Doe
Subject: Re: E-Mail headers
Date: Wed, 22 Aug 2012 23:42:00 +0200
To: Jane Doe

Answer 1

I'd use a different syntax for the cases of one address and multiple addresses:

\documentclass{article}
\usepackage[T1]{fontenc}
\makeatletter
\newif\if@emailenv
\newenvironment{emails}[1][\ignorespaces]
  {\set@email@separator{#1}\@emailenvtrue\begin{flushleft}}
  {\end{flushleft}}
\def\set@email@separator#1{%
  \def\email@separator{#1\def\email@separator{,}}}
\newcommand{\@email}[2][]{%
  \if@emailenv\else\begin{flushleft}\fi
  \email@separator\space
  \if\relax\detokenize{#1}\relax\else"#1" \fi
  \texttt{<#2>}%
  \if@emailenv\ignorespaces\else\end{flushleft}\fi
}
\newcommand{\email}{%
  \if@emailenv\else\set@email@separator{\ignorespaces}\fi\@email}
\newcommand{\emailTo}{%
  \if@emailenv\else\set@email@separator{\textbf{To:}}\fi\@email}
\newcommand{\emailFrom}{%
  \if@emailenv\else\set@email@separator{\textbf{From:}}\fi\@email}
\newcommand{\emailsFrom}{\emails[\textbf{From:}]}
\newcommand{\emailsTo}{\emails[\textbf{To:}]}
\let\endemailsFrom\endemails
\let\endemailsTo\endemails
\makeatother

\begin{document}
\email{pippo@stackexchange.com}

\email[Doe, John]{john.doe@stackexchange.com}

\emailTo{pippo@stackexchange.com}

\emailTo[Doe, John]{john.doe@stackexchange.com}

\emailFrom{pippo@stackexchange.com}

\emailFrom[Doe, John]{john.doe@stackexchange.com}



\begin{emails}
\email{pippo@stackexchange.com}
\email[Doe, John]{john.doe@stackexchange.com}
\email[Doe, Jane]{jane.doe@stackexchange.com}
\end{emails}

\begin{emailsTo}
\email{pippo@stackexchange.com}
\email[Doe, John]{john.doe@stackexchange.com}
\email[Doe, Jane]{jane.doe@stackexchange.com}
\end{emailsTo}

\begin{emailsFrom}
\email{pippo@stackexchange.com}
\email[Doe, John]{john.doe@stackexchange.com}
\email[Doe, Jane]{jane.doe@stackexchange.com}
\end{emailsFrom}

\end{document}

Answer 2

This solution uses foreach from TikZ / PGF. You specify the names and mails as a list of the form name/mail,name/mail and so on:

The Code

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}
\usepackage{xifthen}

\newcommand{\toString}{\textbf{To:} }

\newcommand{\emailto}[1]% list ; "/" separates mail and name, "," separates people
{   \xdef\maillist{}% empty maillist
    \foreach \x/\y [count=\c] in {#1}% for each iteration over the name/mail list, increase \c by one
    {   \ifthenelse{\c=1}% if first iteration... 
            {\xdef\addcomma{}}% leave out comma
            {\xdef\addcomma{,}}% else put one
        \ifthenelse{\equal{\x}{}}% if no name given
            {\xdef\maillist{\maillist\addcomma$<$\y$>$}}% put just <mail>
            {\xdef\maillist{\maillist\addcomma"\x"$<$\y$>$}}% else put "name"<mail>
    }
    \toString\maillist% output of the final list
}

\begin{document}

\emailto{John Doe/John.Doe@a.bc,Jane Dane/Jane.Dane@way.ne,/Denny.Crane@law.com}

\end{document}

The Result

---

Edit 1: A little generalization: Now you can reuse \email for other definitions. I have no idea how to do this with with optional parameters, as their number is not equal to the parameters.

The Code

\newcommand{\email}[1]% list ; "/" separates mail and name, "," separates people
{   \xdef\maillist{}% empty maillist
    \foreach \x/\y [count=\c] in {#1}% for each iteration over the name/mail list, increase \c by one
    {   \ifthenelse{\c=1}% if first iteration... 
            {\xdef\addcomma{}}% leave out comma
            {\xdef\addcomma{,}}% else put one
        \ifthenelse{\equal{\x}{}}% if no name given
            {\xdef\maillist{\maillist\addcomma$<$\y$>$}}% put just <mail>
            {\xdef\maillist{\maillist\addcomma"\x"$<$\y$>$}}% else put "name"<mail>
    }
}

\newcommand{\emailto}[1]
{   \email{#1}
    \textbf{To: }\maillist
}

\newcommand{\emailfrom}[1]
{   \email{#1}
    \textbf{From: }\maillist
}

The Result

\emailto{John Doe/John.Doe@a.bc,Jane Dane/Jane.Dane@way.ne,/Denny.Crane@law.com}

\emailfrom{John Doe/John.Doe@a.bc,Jane Dane/Jane.Dane@way.ne,/Denny.Crane@law.com}

---

Edit 2: And Now for Something Completely Different:
This solution uses xstring, the list format is (name)email;.
Please note that you also have to terminate the list with a semicolon ;

The Code

\documentclass[parskip]{scrartcl}
\usepackage[margin=10mm]{geometry}
\usepackage{xifthen}
\usepackage{xstring}
\usepackage{xcolor}

\newcommand{\email}[1]% (<name>)<email>;(<name>)<email>
{   \xdef\mylist{#1} % set mylist to the input
    \xdef\myentry{} % empty myentry
    \xdef\myname{} % empty myname
    \xdef\myemail{} % empty myemail
    \xdef\myoutput{} % empty myoutput
    \xdef\mynumber{} % empty mynumber
    \StrBefore{\mylist}{;}[\myentry]  % get everything in mylist before ; and save it to myentry, so this should be the first person, e.g (name)mail
    \StrLen{\myentry}[\mynumber] % save length of myentry to mynumber
    \whiledo{\mynumber>0} % while myentry is not empty (e.g. length > 0)
    {   \StrBetween{\myentry}{(}{)}[\myname] % extract what is between ( and ) in myentry and save it to myname
        \StrPosition{\myentry}{)}[\mynumber] % save position of ) to mynumber
        \ifthenelse{\mynumber>0} % if the character ) is found in myentry
            {   \StrBehind{\myentry}{)}[\myemail]} % then get everything behind ), e.g the email
            { \xdef\myemail{\myentry}}% otherwise (e.g. no name present) set myemail to myentry
        \StrLen{\myname}[\mynumber] % set mynumber to the length of mynem
        \ifthenelse{\mynumber>0} % if length of myname is non-zero (e.g one was provided)
            {   \xdef\myoutput{\myoutput"\myname"$<$\myemail$>$}} % then print "name"<mail>
            { \xdef\myoutput{\myoutput$<$\myemail$>$}}  % else print <mail>
        \StrBehind{\mylist}{;}[\mylist] % delete everything up to the first ; e.g the entry that was just worked with
        \StrBefore{\mylist}{;}[\myentry] % new myentry is everything before the next ;
        \StrLen{\myentry}[\mynumber] % determine length of myentry and save that number to mynumber
        \ifthenelse{\mynumber>0} % if a new myentry is present (e.g not end of list)
            {   \xdef\myoutput{\myoutput,}} % then add a comma
            {} % else do nothing
        }
    %\myoutput  % after all entrys were processed, output the result
}

\newcommand{\eMailTo}[1]%
{   \email{#1}
    \textbf{To: }\myoutput
}

\newcommand{\eMailFromColor}[2][green!50!gray]%
{   \email{#2}
    \textcolor{#1}{\textbf{From: }\myoutput}
}

\begin{document}

\eMailTo{(Doe, John)John.Doe@a.bc;(Dane, J. A. N. E)Jane.Dane@way.ne;Denny.Crane@law.com;}

\eMailFromColor{(Doe, John)John.Doe@a.bc;(Dane, J. A. N. E)Jane.Dane@way.ne;Denny.Crane@law.com;}

\eMailFromColor[red!80!black]{(Doe, John)John.Doe@a.bc;(Dane, J. A. N. E)Jane.Dane@way.ne;Denny.Crane@law.com;}

\end{document}

The Result