Modify "mailto:" with alias and domain

[PainSled]

I suggest adding an option change to the "mailto:" link on /mailbox, as it would be quite convenient.

This could be done with an additional field in /settings, next to every alias input, and a radio button to specify main link address. Settings menu for an example mailbox called "735randomname", could look something like this:

○ 735randomname＠mailnesia.com (Default)
◉ [ janedoe   ] [ alt-dom.com ] [ Ok ] [ Delete ]
○ [ johndoe    ] [         ] [ Ok ] [ Delete ]