To simplify the use of your SMTP Auth Relay, we recommend creating a separate account in your Thunderbird email client. This separate account has both an IMAP and SMTP server.  

If you are a user of the MailRoute Managed Email Membership Service (MEMS) (such as a member of a professional organization or alumni group) and using only the MEMS email forwarding service, the IMAP account will not store any of your email - it will be forwarded appropriately.

Users of the MailRoute Hosted Email Service have full IMAP mailbox and storage capabilities.

TL;DR (Too Long, Didn't Read)

Gather the info from our Control Panel by clicking the SMTP Auth Relay tab on the left menu.  You'll have to click the eye icon to view your passwords.  If you don't have a local password set up, you'll be asked to create one.  The Inbound (IMAP) and Outbound (SMTP) servers may have different logins and will have different passwords.   Go into your Mail.app, add a new account using those settings.

When you send email, click the From address to choose your new account for sending email.  It'll pass SPF, DKIM, DMARC checks.  Congratulations!

Long Version

Gather the info you need to configure your email client

To configure your email client to use the MailRoute SMTP Auth Relay service for outbound email relay, you will need to gather some info from the MailRoute Control Panel and then configure your email client. 

1. Login to admin.mailroute.net and click the My Settings link at the top of the page.
   
   
2. Click the SMTP Auth Relay tab in the Settings menu on the left side of the page. 
   
   
   
   
3. Gather your info!  You can click the copy icon  to copy the values of any field.
   
   There are separate Inbound (IMAP) Server and Outbound (SMTP) Server configurations.  You'll need both:
   
   
   Inbound (IMAP) Server Password:  Click the eye icon to display your password .  If you haven't set a local MailRoute password yet, you will be prompted to do so.   Your Inbound (IMAP) Server password may be the same as your Control Panel login password.  You'll be shown this, if this is the case.  
   
            
   
   Outbound (SMTP) Server Password:  Click the eye icon to display your password. Accept the Terms of Service:
   
            
   
   By the way, you can generate a new password for your Outbound (SMTP) Server at any time.

Configure your email client

1. Open your Thunderbird email client.  Select the Settings icon on the lower left, and then the Account Settings button..
   
   
2. Click Account Actions and then Add Mail Account... from the popup menu:
   
   
   
   
3. Enter your full name, email address, and Inbound (IMAP) Password.   Then click the configure manually link.
4. Enter in the Server settings that you gathered earlier.
   
   Incoming Server
        Protocol: IMAP
        Hostname: Your Inbound (IMAP) Server
        Port: 143
        Connection Security: STARTTLS
        Authentication method: Normal Password
        Username: Your Inbound (IMAP) Username
   
   Outgoing Server
        Hostname: Your Outbound (SMTP) Server
        Port: 587
        Connection Security: STARTTLS
        Authentication method: Autodetect
        Username: Your Outbound (SMTP) Login
   
   Then click the Retest button:
   
   
   
5. It should verify all your settings, so you can click the Done button!
   
   
6.  You're all done! Go have fun with your new account!
   
   

Using your new account to send email

When you compose a new email, you'll have a menu where the From address is displayed.  Click it and choose your new account from the popup menu.  That's all there is to it.  The email will come from your new account, and will pass SPF, DKIM, and DMARC checks!