Add ssmtp to handle redirect

Dockerfile

@@ -1,8 +1,9 @@
 FROM alpine:3
 
-RUN apk add --no-cache tini ca-certificates dovecot dovecot-ldap dovecot-lmtpd dovecot-pigeonhole-plugin dovecot-pop3d python3
+RUN apk add --no-cache tini ca-certificates dovecot dovecot-ldap dovecot-lmtpd dovecot-pigeonhole-plugin dovecot-pop3d python3 ssmtp
 
 ADD dovecot.conf /etc/dovecot/dovecot.conf
+ADD ssmtp.conf /etc/ssmtp/ssmtp.conf
 
 VOLUME ["/etc/dovecot", "/srv/mail"]
 ENTRYPOINT ["/sbin/tini", "--"]

ssmtp.conf

@@ -0,0 +1,52 @@
+#
+# /etc/ssmtp.conf -- a config file for sSMTP sendmail.
+#
+
+# The person who gets all mail for userids < MinUserId
+# Make this empty to disable rewriting.
+root=postmaster
+
+# All mail delivered to userid >= MinUserId goes to user, not root.
+#MinUserId=1000
+
+# The place where the mail goes. The actual machine name is required
+# no MX records are consulted. Commonly mailhosts are named mail.domain.com
+# The example will fit if you are in domain.com and your mailhub is so named.
+#mailhub=mail
+mailhub=djehouty.pomail.fr
+
+# Example for SMTP port number 2525
+# mailhub=mail.your.domain:2525
+# Example for SMTP port number 25 (Standard/RFC)
+# mailhub=mail.your.domain
+# Example for SSL encrypted connection
+# mailhub=mail.your.domain:465
+
+# Where will the mail seem to come from?
+#rewriteDomain=
+
+# The full hostname
+
+# Gentoo bug #47562
+# Commenting the following line will force ssmtp to figure
+# out the hostname itself.
+
+# hostname=_HOSTNAME_
+
+# Set this to never rewrite the "From:" line (unless not given) and to
+# use that address in the "from line" of the envelope.
+#FromLineOverride=YES
+
+# Use SSL/TLS to send secure messages to server.
+#UseTLS=YES
+
+# Use SSL/TLS certificate to authenticate against smtp host.
+#UseTLSCert=YES
+
+# Use this RSA certificate.
+#TLSCert=/etc/ssl/certs/ssmtp.pem
+
+# Get enhanced (*really* enhanced) debugging information in the logs
+# If you want to have debugging of the config file parsing, move this option
+# to the top of the config file and uncomment
+#Debug=YES