mutt SMTP TLS error sending mail

Question

When I try to send a mail, I get the following error:

gnutls_handshake: An unexpected TLS packet was received.

This is my .muttrc (myname, myaddress and mymail are placeholders):

# Automatically log in to this mailbox at startup
set imap_user="myname"
set imap_pass=""
set spoolfile="imaps://imap.myaddress/Inbox"
set folder="imaps://imap.myaddress/Inbox"
set record="=Sent"
set postponed="=Drafts"

# define how to send mails
set smtp_url="smtps://$imap_user:[email protected]:587"

# activate TLS if available on the server
set ssl_starttls=yes

# always use SSL when connecting to a server
set ssl_force_tls=yes

# wait to enter mailbox manually
set imap_passive

# Automatically poll subscribed mailboxes for new mail (new in 1.5.11)
set imap_check_subscribed

# Reduce polling frequency to a sane level
set mail_check=60

# And poll the current mailbox more often (not needed with IDLE in post 1.5.11)
#set timeout=10

# keep a cache of headers for faster loading (1.5.9+?)
#set header_cache=~/.hcache

# Display download progress every 5K
set net_inc=5

# Cancel a message when subject is blank
set abort_nosubject=yes

# Set default editor
set editor="gvim -v"

# Asks to include message when replying
set include=ask-yes

# Asks to postpone a message when not sent
set postpone=ask-yes

# Ask before printing
set print=ask-yes

# set from to ensure mutt doesn't put [email protected] 
set from="myemail"
set use_from=yes
set envelope_from="yes"

Answer 1

When using smtp submission on port 587, the value for smtp_url should start with "smtp://", i.e. not with "smtps://". It is also important to make sure ssl_starttls is set to "yes", as correctly done in the config above.

While setting up my own server I got the exact same problem. Having access to logs on both the client & the server side, made it obvious that it surely was a client side issue.

A config option starting with smtps tells mutt to open a ssl encrypted connection to the server. However the server is expecting a clear text smtp session which transfers to become encrypted as soon as the client & server have done some negotiation.