John Doe
john@example.com Jane Doe
jane.doe@example.com

John Doe          Jane Doe
john@example.com  jane@example.com

documentclass{beamer}
useoutertheme{infolines}
title{Title}
author[J.,Doe & J.,Doe]
{%
  texorpdfstring{
    begin{columns}%[onlytextwidth]
      column{.45linewidth}
      centering
      John Doe\
      href{mailto:john@example.com}{john@example.com}
      column{.45linewidth}
      centering
      Jane Doe\
      href{mailto:jane.doe@example.com}{jane.doe@example.com}
    end{columns}
  }
  {John Doe & Jane Doe}
}
begin{document}
begin{frame}
  titlepage
end{frame}
end{document}

newcommand{newauthor}[2]{
  parbox{0.26textwidth}{
    texorpdfstring
      {
        centering
        #1 \
        {scriptsize{urlstyle{same}url{#2}urlstyle{tt}}}
      }
      {#1}
  }
}

...

author{
  newauthor{John Doe}{john@example.com}
and
  newauthor{Jane Doe}{jane@example.com}
}

documentclass{beamer}
usepackage{lmodern}

%-------------------------------------------------
% title page with two authors
makeatletter
setbeamertemplate{title page}{
centering
begin{beamercolorbox}[rounded=true,shadow=true,sep=8pt,center]{title}
usebeamerfont{title}inserttitlepar%
      ifxinsertsubtitle@empty%
      else%
        vskip0.25em%
        {usebeamerfont{subtitle}usebeamercolor[fg]{subtitle}insertsubtitlepar}%
      fi%
end{beamercolorbox}
vfill
begin{beamercolorbox}{author}
begin{columns}[T]
column{.28textwidth}%
centering
usebeamerfont{author}John Doe\
john@example.com
column{.25textwidth}%
centering
usebeamerfont{author}Jane Doe\
jane@example.com
end{columns}
end{beamercolorbox}
vfill
usebeamerfont{institute}insertinstitute par
vfill
centering
usebeamerfont{date}insertdatepar
vfill
begin{beamercolorbox}[center]{titlegraphic}
inserttitlegraphic
end{beamercolorbox}
}
makeatother

title{My title}
subtitle{my subtitle}
institute{My institute}

begin{document}
begin{frame}
titlepage
end{frame}

end{document}