How to use MailChannels as a Smarthost

Introduction

It's becoming more common for data centers to restrict emails from sending over port 25. Mailchannel is another Smarthost provider that allows mail to be sent over an alternative port using Exim. 

Procedure

To use MailChannels, you will need to configure Exim to authenticate with MailChannels using the credentials they provide you.

1. Sign up for MailChannels
   MailChannels  
2. Log in to WHM, and navigate to "WHM / Service Configuration / Exim Configuration Manager / Advanced Editor." On this page, search for "Section: AUTH". In the text box, input the following:
3. In the Section: AUTH area, add:

   • mailchannels_login:
      driver = plaintext
      public_name = LOGIN
      client_send = : MailChannelsUsername : MailChannelsPassword

   • Replace MailChannelsUsername and MailChannelsPassword with the username and password provided by MailChannels.
4. Next, go to the "Section: POSTMAILCOUNT" section, and input the following:
   Please note that if outbound TCP port 25 is blocked, you will have to replace the port number on the route_list line with 2525 or 587.
   
   • On v108 or above:
     

     send_via_mailchannels:
       driver = manualroute
       domains = ! +local_domains : ! +manualmx_domains
     .ifdef SRSENABLED
      # if outbound, and forwarding has been done, use an alternate transport
      transport = ${if eq {$local_part@$domain} \
               {$original_local_part@$original_domain} \
               {mailchannels_smtp} {mailchannels_forwarded_smtp}}
     .else
      transport = mailchannels_smtp
     .endif
     route_list = * smtp.mailchannels.net::25 randomize byname

   • On v106 or below:
     

     send_via_mailchannels:
      driver = manualroute
      transport = mailchannels_smtp
      domains = ! +local_domains : ! +manualmx_domains
      route_list = * smtp.mailchannels.net::25 randomize byname

5. Then go to the "Section: TRANSPORTSTART" section. Input the following into the text box:
   

   mailchannels_smtp:
    driver = smtp
    hosts_require_auth = *
    tls_tempfail_tryclear = true
    headers_add = X-AuthUser: ${if match {$authenticated_id}{.*@.*}\
       {$authenticated_id} {${if match {$authenticated_id}{.+}\
       {$authenticated_id@$primary_hostname}{$authenticated_id}}}}
    dkim_domain = ${perl{get_dkim_domain}}
    dkim_selector = default
    dkim_canon = relaxed
    dkim_private_key = "/var/cpanel/domain_keys/private/${dkim_domain}"
    message_linelength_limit = 2048

6. Additionally, on servers running v108 or above, add the following to the TRANSPORTSTART section as well:
   

   .ifdef SRSENABLED
   mailchannels_forwarded_smtp:
    driver = smtp
    hosts_require_auth = *
    max_rcpt = 1
    return_path = ${srs_encode {SRS_SECRET} {$return_path} {$original_domain}}
    tls_tempfail_tryclear = true
    headers_add = X-AuthUser: ${if match {$authenticated_id}{.*@.*}\
       {$authenticated_id} {${if match {$authenticated_id}{.+}\
       {$authenticated_id@$primary_hostname}{$authenticated_id}}}}
    dkim_domain = ${perl{get_dkim_domain}}
    dkim_selector = default
    dkim_canon = relaxed
    dkim_private_key = "/var/cpanel/domain_keys/private/${dkim_domain}"
   .endif

7. Go to the bottom of the page and click "Save." The changes will be added to the Exim configuration and automatically restart the Exim service.
8. Try sending a test email using one of the Webmail applications. If the email does not leave the server, you must examine the /var/log/exim_mainlog file to determine the cause of the issue.

Mailing Lists

If you use mailing lists,  you must also configure the following in "mailman_virtual_transport". 

Within the Exim Advanced Editor, scroll down to "Add additional configuration setting" and then add "mailman_virtual_transport."

headers_add = "X-MC-MailingList: $original_local_part@$original_domain\n"

mailman_virtual_transport:
   driver = pipe
   command = /usr/local/cpanel/3rdparty/mailman/mail/mailman \
   '${if def:local_part_suffix \
   {${sg{$local_part_suffix}{-(\\w+)(\\+.*)?}{\$1}}} \
   {post}}' \
   ${lc:$local_part}_${lc:$domain}
   current_directory = /usr/local/cpanel/3rdparty/mailman
   home_directory = /usr/local/cpanel/3rdparty/mailman
   user = mailman
   group = mailman
   headers_add = "X-MC-MailingList:$original_local_part@$original_domain\n"

Once everything has been configured, click save.

Additional Resources

The following article covers the reason that hosting providers typically block access to port 25:

How To Send Email When Your Server Provider Blocks Port 25?

MailChannels does offer a plugin that allows for quick configuration options. For details, please refer to their official documentation at:

MailChannels cPanel & WHM plugin for Outbound Filtering 

MailChannels cPanel & WHM Plugin for Inbound Filtering