remote_login:
  driver = plaintext
  public_name = LOGIN
  client_send = : user : password

${extract{auth_pass}{${lookup{$sender_address_domain}wildlsearch{/etc/exim/smtp_auths}{$value}fail}}}

example.com: auth_pass=password

${lookup mysql{SELECT users.remote_secret as secret FROM users WHERE users.domain='${quote_mysql:$sender_address_domain}'}{$value}}

[ec2-user@ip-172-31-16-5 exim]$ sudo exim -be -Mset <message-id>
> ${extract{auth_pass}{${lookup{$sender_address_domain}wildlsearch{/etc/exim/smtp_auths}{$value}fail}}}
password
> ${lookup mysql{SELECT users.remote_secret as secret FROM users WHERE users.domain='${quote_mysql:$sender_address_domain}'}{$value}}
password
>

${quote_mysql:$sender_address_domain}

example.com