Msmtp

apt-get install msmtp msmtp-mta mailutils
ln -s /usr/bin/msmtp /usr/sbin/sendmail
touch /var/log/msmtprc && chmod 666 /var/log/msmtprc
chmod 600 ~/.msmtprc

ou em /etc/msmtprc

gmail

# Set default values for all following accounts.
defaults
logfile /var/log/msmtp.log
port 587
tls on
tls_trust_file /etc/ssl/certs/ca-certificates.crt

# gmail account
account gmail
host smtp.gmail.com
auth on
port 587
user your.account@gmail.com
password yourpassword
from your.account@gmail.com
#aliases        /etc/aliases
#tls_trust_file /usr/share/ca-certificates/mozilla/Equifax_Secure_CA.crt

Locaweb

defaults
tls on
tls_starttls on
tls_trust_file /etc/ssl/certs/ca-certificates.crt

#logfile ~/.msmtp.log
logfile /var/log/msmtp.log

# The SMTP servers
account locaweb
host email-ssl.com.br
from contato@seudominio.com.br
auth login
user contato@seudominio.com.br
password suasenha
port 587

# Set a default account
account default : locaweb

PHP

sendmail_path = "/usr/bin/msmtp -C /etc/msmtprc -t"

Referencias

• https://www.dicas-l.com.br/arquivo/enviar_email_com_msmtp.php
• https://wiki.archlinux.org/index.php/Msmtp
• https://gist.github.com/JosefJezek/6194563
• https://www.sylvaindurand.org/send-emails-with-msmtp/
• https://wiki.debian.org/msmtp
• https://websistent.com/how-to-use-msmtp-with-gmail-yahoo-and-php-mail/
• https://decatec.de/linux/linux-einfach-e-mails-versenden-mit-msmtp/