I don't know if this is related to the other issue I was having with my mailbox not being found which I fixed in the other blog post, but after installing postfix:

sudo apt install postfix

and correctly configuring the SMTP relay, I could send email using the sendmail function:

sendmail youremail@gmail.com
Subject: testing
does it work!
.

but i just couldn't use my normal command mail:

echo "email message text" | mail -s "subject line" "youremail@gmail.com"

which I find far more friendly than the sendmail way.

anyhow the fix was to install mailutils:

sudo apt install mailutils

works a treat,

So if you want to install postfix and mutt you should use:

sudo apt install postfix mutt libsasl2-modules mailutils