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Email with subject containing: [CAUTION: UNTRUSTED SOURCE]

If you receive an email with [CAUTION: UNTRUSTED SOURCE] in the subject line, that means the email has failed Sender Policy Framework (SPF) verification.

CalTel will NEVER ask for your username, password, credit card numbers or any other personal information over email.

SPF is a widely adopted industry standard to reduce spam and email spoofing that is deployed in two parts.

  1. Every domain publishes a public list of email servers that are authorized to send email for that domain.
  2. Incoming email messages are compared the list of authorized senders.

We have had step one completed for years now and are moving onto step 2 and will begin enforcing published senders.

This is in response to several massive phishing attacks against CalTel customers, where random internet devices across the internet started sending email to our customers trying to steal information.

Most large ISPs have been enforcing SPF for a while now, but they all do it in different ways. Some will deny or delete the message. Some will put the message into the spam folder or quarantine.

At this point in time, if CalTel receives a message that is in clear violation of published SPF records, the message will have the subject altered as you see.

In the future, those messages will be quarantined or flat out denied.

SPF is the senders responsibility. If you are a CalTel customer, and the messages you are sending are being tagged that way, your outgoing mail server needs to be changed:

See General Email Settings

In you are not a CalTel customer, you will probably need to contact your ISP to verify your mail settings.

If you host your own domain, you need to adjust your DNS published SPF records.

Please see for more details on the protocol.

internet_security/untrusted_source_emails.txt · Last modified: 2014/10/27 08:27 by cybarra