What is Carrier Filtering?

Carrier Filtering is the process by which mobile carriers (AT&T, T-Mobile, Verizon, and others) automatically screen inbound A2P text messages and block or divert those they determine to be spam, non-compliant, or from untrustworthy senders. Filtering happens at the carrier network level before messages reach the recipient's phone.

Carrier filtering has become increasingly aggressive as SMS spam has grown. Carriers use machine learning, content analysis, sender reputation scoring, and registration checks to evaluate each message. Messages that fail these checks may be silently dropped (the sender isn't notified), delayed, or flagged.

For legitimate businesses, carrier filtering is both a protection (it keeps the SMS channel clean and trustworthy) and a challenge (legitimate messages can sometimes be caught in filters, especially for new or improperly registered senders).

Carriers evaluate A2P messages across several dimensions. Sender registration: is the sender registered through 10DLC or another approved channel? Unregistered senders are heavily filtered. Content analysis: does the message contain spam indicators like excessive links, URL shorteners, or flagged keywords? Sending patterns: is the sender showing spam-like behavior like sudden volume spikes or high message-to-response ratios? Complaint rate: are recipients reporting these messages as spam?

Each carrier has its own filtering algorithms and thresholds. A message that passes T-Mobile's filters might be caught by AT&T's. Filtering is non-transparent — carriers don't disclose their exact rules, and messages are often silently dropped without notification.

The most reliable way to avoid filtering is proper 10DLC registration, consistent sending patterns, TCPA-compliant content, and healthy subscriber engagement.

Carrier filtering is the invisible threat to SMS programs. You can write the perfect message, target the right segment, and schedule at the optimal time — but if the carrier filters it, none of that matters. The message simply disappears.

For SMS commerce, filtered messages mean lost revenue. If a drop announcement is filtered for 5% of your list, that's 5% of potential sales you never had a chance at. For time-sensitive drops where inventory is limited, this is particularly costly.

Maintaining low filtering rates requires ongoing attention: proper registration, clean content, consistent volume patterns, and responsive opt-out handling. SMS platforms handle much of the technical infrastructure, but brands are responsible for content quality and compliance.