It's not very often but sometimes I have to update SharePoint user email in profile. Here's a simple powershell code to do it.

#update SPUser email 

if ((Get-PSSnapin "Microsoft.SharePoint.PowerShell" -ErrorAction SilentlyContinue) -eq $null) 
{ 
    Add-PSSnapin Microsoft.SharePoint.PowerShell 
} 

$webUrl = "https://spdev" 
$spweb = Get-SPWeb $webUrl 

$userlogin = "mydomain\userLogin" 
$newUserEmail = "Name.LastName@mycompany.com" 
Set-SPUser -Identity $userlogin -Email $newUserEmail -Web $webUrl 


#Let's check that everything's ok 
$user = Get-SPUser -Identity  $userlogin -Web $webUrl 
Write-Host $user.Email