Set default sender or list of default senders with Emacs

[PlasmaShift]

When using Emacs and notmuch-mua-new-mail function the sender always defaults to my
email@fastmail instead of
email@customdomain which is what I use and keep changing it to
Grabbing the sender emails address from jmap or Fastmail would be best
If not possible is their a way of to set this to a default value or list of values?

compose-mail command takes the value of user-mail-address for sender address while notmuch-mua-new-mail does not

Potential related issues #33 #35 #30

As a side note is their a way to set compose-mail command to notmuch-mua-new-mail
for other Emacs apps that use mail commands? or other commands to set to use Notmuch?