Hosted Exchange: Forwarding to External Address

Background:

In some cases, you may desire to have emails sent to you forwarded to an external email address (such as Gmail, Hotmail, Yahoo, etc.). In years past, this was accomplished by a redirect rule on the server, which redirect emails sent to a specific email address to another external address. However, with the introduction of email security technologies such as SPF and DMARC, which are intended to prevent email spoofing, email redirects are becoming problematic.

With an email redirect, the mail server receives the email and redirects it to another external server, leaving the sender's ("From") address intact. Technically, the mail server is spoofing the original sender. For example, let's assume John at Contoso Corp. has his email set to automatically redirect all company emails to his personal Gmail address. In this example, when Bob@Acme.com sends an email to John@Contoso.com, the server for Contoso.com redirects the email to John@Gmail.com, without modifying the sender ("From") address. When Gmail receives the message, it appears to be from Bob@Acme.com - - however, Acme system administrators have created SPF and DMARC records that tell other email servers (such as Gmail) to only accept emails from a list of authorized servers when the sender ("From") address ends in @Acme.com. Since the Contoso email server is not on the list of authorized servers for Acme Corp, Gmail rejects that redirected email. Not all organizations have adopted email security policies, such as SPF and DMARC, so this behavior will appear intermittent to John. As more and more organizations start adopting proper email security policies, more and more emails will be rejected by John's personal Gmail address.

One way around this is for John to configure his Contoso company email account to store-and-forward emails. In this configuration, the mail server for Contoso will accept the email sent from Bob@Acme.com. Then, a couple of seconds later, John's email account will forward that email to his personal Gmail account. This time, Gmail sees the sender ("From") address as John@Contoso.com, which means the Contoso mail server is no longer spoofing the Bob@Acme.com address and the email is delivered properly to John's personal Gmail account.

There is a potential downside to this approach: The sender ("From") address will now be John@Contoso.com. While the subject and the contents of the message are still present, if John tries to reply to this email from his personal Gmail address, the reply will be sent to John's Contoso email address (rather than the original sender, Bob@Acme.com). In this case, John has two options:
  - Log in to his work email and reply to Bob from there. This way, the reply button functions as expected, and the sender ("From") address that Bob will see is John's company email address.
  - Reply to Bob's email from the personal Gmail account but before sending the message, manually type Bob's email address in the recipient ("To") field. Keep in mind that Bob will see John's personal Gmail email address, and may start corresponding in the future directly to John's personal Gmail address, which may be unprofessional, unwanted, or against company policy.

Configure an External Email Forwarder:

To set up an Email Forwarder within your Exchange mailbox, follow the instructions detailed below:
1) Log in to Outlook Web Access.
2) Click the settings (gear) icon in the upper-right corner and select Options.
3) Navigate to Mail > Automatic Processing > Inbox and sweep rules.
4) Under the Inbox Rules section, click the + icon to add a new rule.
5) Enter a name for the new rule, such as: Forward to Personal Email Account.
6) Under the "When a message arrives, ..." drop-down, select the "[Apply to all messages]" option.
7) Under the "Do all of the following" drop-down, select the "Forward, redirect, or send > Forward the message to..." option.
8) In the "Forward the message to..." text field at the top, enter the email address you would like inbound messages forwarded to and click Save.
9) You may optionally add another action under the "Do all of the following" drop-down to "Delete the message", if you have no desire to keep a copy of the email within your Exchange mailbox.
10) Click the "OK" button at the top to create the new rule.
11) Click the "Save" button at the top to save the list of rules.