Can iPhone autofill emails in contacts based on pattern?
I found a way to make it happen.
There may be easier ways to do it but this is what I found.
I think this solution will work well with iPhone, Android and Windows phones as it's not an app.  

Our contacts sync with our mail office365 OWA.
And in Office 365 you can export contacts as a CSV file.  

Once you have the CSV you can open it with Excel and create a formula to build the email.
Since I'm swedish I need to remove ÅÄÖ and make them AO I did that with substitute().
Example:  

=Substitute(Substitute(Substitute(A2;"Å";"A");"Å";"A");"Ö";"O")


The above formula can change names with ÅÄÖ, for example Åsa becomes Asa.
If you are Spanish you may need to replace for example ñ to n.  

Because the layout of a CSV can be different depending on mail client and you may have a different language Excel installed there is no point in typing out the full formula.  

But if the above formula is for first name you can add on last name like this:  

=Substitute(Substitute(Substitute(A2;"Å";"A");"Å";"A");"Ö";"O")&amp;"."&amp;Substitute(Substitute(Substitute(B2;"Å";"A");"Å";"A");"Ö";"O")


If column A is first name and B is last name.
Also usually capital letters are "unwanted" in emails, you can use function Lower() to make capital => lowercase letters.  

It worked very well at last and I could easily upload the edited contacts CSV and it was synced to my phone.