Q: We have an employee that works from home. Some of our clients don't receive this person’s email messages, but other clients, and our internal users, receive his email messages. Why aren’t some outside parties receiving email messages from our telecommuter?
A: From the information provided, I would guess that the Sender Policy Framework (SPF) is preventing some clients from getting his email messages. I bet the telecommuter in question uses his home ISP’s SMTP server for sending outgoing email messages from his company email address. I also bet that your domain’s DNS zone file has an SPF record, which defines all the authorized SMTP servers for your domain. If that's the case, I’ll explain what’s happening after first providing some background about how email servers identify the appropriate SMTP servers for a given DNS domain.
To receive email for a domain, the domain’s owner must publish one or more mail exchanger (MX) records in the DNS's zone file, which identifies email servers that can receive email messages for that domain. Note that MX records are mandatory. There's a second type of email record that's much newer than DNS MX records and is optional: SPF records, which let a domain’s owner publish information about which SMTP servers other servers should trust when receiving email messages from that domain. With SPF, you can publish all the email servers that your company legitimately uses to send email messages from your domain. Other companies, such as your clients, might configure their email servers to check SPF records on incoming email messages. . . .
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