This is my favorite kind of question!
Update
If you get some nice icons related to emails, then you can add them to the design (I got some icons from iconfinder for my example). Here's the tcolorbox version (see below) with an icon bar added:

The code:
\documentclass{memoir}
\usepackage{graphicx}
\usepackage[many]{tcolorbox}
\usetikzlibrary{positioning}
\usepackage{lipsum}% to generate text for the example
\definecolor{myboxgray}{RGB}{216,207,190}
\definecolor{mybackgray}{RGB}{243,232,223}
\definecolor{mybargray}{RGB}{192,185,169}
\newcommand\mybox[1]{
\node[text width=2cm] {\strut#1};
}
\tikzset{
mybox/.style={
draw=myboxgray!70!black,
fill=myboxgray,
text width=1.3cm,
anchor=north west,
align=center,
inner ysep=2pt,
font=\sffamily\small
},
myinfobox/.style={
draw=myboxgray!70!black,
text width=\textwidth-2cm-1pt,
anchor=north west,
inner ysep=2pt,
fill=white,
font=\sffamily\small
},
mybar/.style={
draw=mybargray!70!black,
fill=mybargray,
text width=\textwidth-0.666em,
minimum height=20pt,
anchor=south west,
outer sep=0pt
}
}
\newtcolorbox{mytemail}[5][]{
breakable,
pad after break=-63pt,
freelance,
colback=white,
left=0pt,
right=0pt,
outer arc=0pt,
arc=0pt,
colframe=gray,
colback=mybackgray,
boxrule=0.5pt,
top=80pt,
left=4pt,
right=4pt,
before=\par\vskip26pt,
fontupper=\sffamily\small,
overlay unbroken and first={
\draw[draw=myboxgray!70!black,fill=mybargray]
([yshift=20pt]frame.north west)
rectangle
(frame.north east);
\node[anchor=west]
at ([yshift=9pt]frame.north west)
(send) {\includegraphics[height=14pt]{send}};
\node[anchor=west,font=\sffamily\small]
at (send.east)
(sendtext) {Send};
\node[anchor=west]
at ([xshift=10pt]sendtext.east)
(cancel) {\includegraphics[height=14pt]{cancel}};
\node[anchor=west,font=\sffamily\small]
at (cancel.east)
(canceltext) {Cancel};
\node[anchor=west]
at ([xshift=10pt]canceltext.east)
(save) {\includegraphics[height=14pt]{save}};
\node[anchor=west,font=\sffamily\small]
at (save.east)
(savetext) {Save Draft};
\node[anchor=west]
at ([xshift=10pt]savetext.east)
(add) {\includegraphics[height=14pt]{attachment}};
\node[anchor=west,font=\sffamily\small]
at (add.east)
(addtext) {Add Attachment};
\node[mybox]
at ([shift={(2pt,-2pt)}]frame.north west)
(from) {\strut From:};
\node[mybox,below=2pt of from]
(to) {\strut To:};
\node[mybox,below=2pt of to]
(date) {\strut Date:};
\node[mybox,below=2pt of date]
(subj) {\strut Subject:};
\node[draw,myinfobox,right=2pt of from]
(fromtext) {\strut #2};
\node[draw,myinfobox,right=2pt of to]
(totext) {\strut #3};
\node[draw,myinfobox,right=2pt of date]
(datetext) {\strut #4};
\node[draw,myinfobox,right=2pt of subj]
(subjtext) {\strut #5};
\draw[myboxgray!70!black,fill=white]
([shift={(2pt,-74pt)}]interior.north west)
rectangle
([shift={(-2pt,2pt)}]interior.south east);
},
overlay middle and last={
\draw[myboxgray!70!black,fill=white]
([shift={(2pt,-2pt)}]interior.north west)
rectangle
([shift={(-2pt,2pt)}]interior.south east);
}
#1
}
\begin{document}
\lipsum[4]
\begin{mytemail}{HamiltonP, Beth}{Croft, Norrie}{September 12th 2014}{Paris}
\lipsum[4]
\end{mytemail}
\lipsum[4]
\end{document}
First version
Here's one possibility in which I simulated the style used for e-mails by some providers. I present two versions; one using tcolorbox and another one using mdframed. Both versions allow page breaks.
First, I used the powerful tcolorbox package:

All the job is done by a mytemail environment with four mandatory arguments:
\begin{mytemail}{<from>}{<to>}{<date>}{<subject>
<text>
\end{mytemail}
an optional argument allows to pass eventual additional options to the tcolorbox defined. The box in the example was produced using
\begin{mytemail}{HamiltonP, Beth}{Croft, Norrie}{September 12th 2014}{Paris}
\lipsum[4]
\end{mytemail}
The code:
\documentclass{memoir}
\usepackage[many]{tcolorbox}
\usetikzlibrary{positioning}
\usepackage{lipsum}% to generate text for the example
\definecolor{myboxgray}{RGB}{216,207,190}
\definecolor{mybackgray}{RGB}{243,232,223}
\newcommand\mybox[1]{
\node[text width=2cm] {\strut#1};
}
\tikzset{
mybox/.style={
draw=myboxgray!70!black,
fill=myboxgray,
text width=1.3cm,
anchor=north west,
align=center,
inner ysep=2pt,
font=\sffamily\small
},
myinfobox/.style={
draw=myboxgray!70!black,
text width=\textwidth-2cm-1pt,
anchor=north west,
inner ysep=2pt,
fill=white,
font=\sffamily\small
}
}
\newtcolorbox{mytemail}[5][]{
breakable,
pad after break=-63pt,
freelance,
colback=white,
left=0pt,
right=0pt,
outer arc=0pt,
arc=0pt,
colframe=gray,
colback=mybackgray,
boxrule=0.5pt,
top=80pt,
left=4pt,
right=4pt,
before=\par\medskip,
fontupper=\sffamily\small,
overlay unbroken and first={
\node[mybox]
at ([shift={(2pt,-2pt)}]frame.north west)
(from) {\strut From:};
\node[mybox,below=2pt of from]
(to) {\strut To:};
\node[mybox,below=2pt of to]
(date) {\strut Date:};
\node[mybox,below=2pt of date]
(subj) {\strut Subject:};
\node[draw,myinfobox,right=2pt of from]
(fromtext) {\strut #2};
\node[draw,myinfobox,right=2pt of to]
(totext) {\strut #3};
\node[draw,myinfobox,right=2pt of date]
(datetext) {\strut #4};
\node[draw,myinfobox,right=2pt of subj]
(subjtext) {\strut #5};
\draw[myboxgray!70!black,fill=white]
([shift={(2pt,-74pt)}]interior.north west)
rectangle
([shift={(-2pt,2pt)}]interior.south east);
},
overlay middle and last={
\draw[myboxgray!70!black,fill=white]
([shift={(2pt,-2pt)}]interior.north west)
rectangle
([shift={(-2pt,2pt)}]interior.south east);
}
#1
}
\begin{document}
\lipsum[4]
\begin{mytemail}{HamiltonP, Beth}{Croft, Norrie}{September 12th 2014}{Paris}
\lipsum[4]
\end{mytemail}
\lipsum[4]
\end{document}
And now using the also powerful mdframed package:

All the job is now done by a mymdemail environment with four mandatory arguments:
\begin{mytemail}{<from>}{<to>}{<date>}{<subject>
<text>
\end{mytemail}
The box in the example was produced using
\begin{mymdemail}{HamiltonP, Beth}{Croft, Norrie}{September 12th 2014}{Paris}
\lipsum[4]
\end{mymdemail}
The code:
\documentclass{memoir}
\usepackage[framemethod=tikz]{mdframed}
\usetikzlibrary{positioning}
\usepackage{lipsum}% to generate text for the example
\definecolor{myboxgray}{RGB}{216,207,190}
\definecolor{mybackgray}{RGB}{243,232,223}
\def\mdfrom{\relax}
\def\mdto{\relax}
\def\mddate{\relax}
\def\mdsubj{\relax}
\tikzset{
mybox/.style={
draw=myboxgray!70!black,
fill=myboxgray,
text width=1.3cm,
anchor=north west,
align=center,
inner ysep=2pt,
font=\sffamily\small
},
myinfobox/.style={
draw=myboxgray!70!black,
text width=\textwidth-2cm-1pt,
anchor=north west,
inner ysep=2pt,
fill=white,
font=\sffamily\small
}
}
\newmdenv[
linecolor=myboxgray!70!black,
innertopmargin=76pt,
splittopskip=19pt,
singleextra={
\node[mybox]
at ([shift={(2pt,-2pt)}]O|-P)
(from) {\strut From:};
\node[mybox,below=2pt of from]
(to) {\strut To:};
\node[mybox,below=2pt of to]
(date) {\strut Date:};
\node[mybox,below=2pt of date]
(subj) {\strut Subject:};
\node[draw,myinfobox,right=2pt of from]
(fromtext) {\strut\mdfrom};
\node[draw,myinfobox,right=2pt of to]
(totext) {\strut\mdto};
\node[draw,myinfobox,right=2pt of date]
(datetext) {\strut\mddate};
\node[draw,myinfobox,right=2pt of subj]
(subjtext) {\strut\mdsubj};
\draw[myboxgray!70!black]
([shift={(2pt,-74pt)}]O|-P) --
([shift={(-2pt,-74pt)}]P) --
([shift={(-2pt,2pt)}]P|-O) --
([shift={(2pt,2pt)}]O) -- cycle;
},
firstextra={
\node[mybox]
at ([shift={(2pt,-2pt)}]O|-P)
(from) {\strut From:};
\node[mybox,below=2pt of from]
(to) {\strut To:};
\node[mybox,below=2pt of to]
(date) {\strut Date:};
\node[mybox,below=2pt of date]
(subj) {\strut Subject:};
\node[draw,myinfobox,right=2pt of from]
(fromtext) {\strut\mdfrom};
\node[draw,myinfobox,right=2pt of to]
(totext) {\strut\mdto};
\node[draw,myinfobox,right=2pt of date]
(datetext) {\strut\mddate};
\node[draw,myinfobox,right=2pt of subj]
(subjtext) {\strut\mdsubj};
\draw[myboxgray!70!black]
([shift={(2pt,-74pt)}]O|-P) --
([shift={(-2pt,-74pt)}]P) --
([shift={(-2pt,2pt)}]P|-O) --
([shift={(2pt,2pt)}]O) -- cycle;
},
middleextra={
\draw[myboxgray!70!black]
([shift={(2pt,-2pt)}]O|-P) --
([shift={(-2pt,-2pt)}]P) --
([shift={(-2pt,2pt)}]P|-O) --
([shift={(2pt,2pt)}]O) -- cycle;
},
secondextra={
\draw[myboxgray!70!black]
([shift={(2pt,-2pt)}]O|-P) --
([shift={(-2pt,-2pt)}]P) --
([shift={(-2pt,2pt)}]P|-O) --
([shift={(2pt,2pt)}]O) -- cycle;
},
]{mdemail}
\newenvironment{mymdemail}[4]
{%
\gdef\mdfrom{#1}%
\gdef\mdto{#2}%
\gdef\mddate{#3}%
\gdef\mdsubj{#4}%
\begin{mdemail}
}
{\end{mdemail}}
\begin{document}
\lipsum[4]
\begin{mymdemail}{HamiltonP, Beth}{Croft, Norrie}{September 12th 2014}{Paris}
\lipsum[4]
\end{mymdemail}
\lipsum[4]
\end{document}