Is there a way of displaying board guests' email addresses, rather than just their Trello username?

[Hayley Evans]

I'm setting up a board with external contractors and asking them to comment on the cards, and it would be useful if rather than just seeing their Trello username, I could also see their email address, to identify which branch they are from.  Is there a way of doing this?  I was hoping it would show their email address on their profile but it doesn't seem to.

[Daydreamer Mike]

You could create a contractors list with their contact details, name, phone, email address, branch etc. set up as custom fields.  When they are added to a card or comment on it, it links to that card as an attachment.