If a text message has a status of “delivered” it means that the patient or non-patient's cell phone carrier has confirmed that the text message was received and delivered to their customer. Common reasons text messages may not be received by the recipient are:
wrong phone number - typo or outdated contact info
the cell phone or destination device is out of range (poor reception or signal, no service)
network issues with the recipient’s cell phone carrier - temporary outages, congestion or routing problems
the cell phone or destination device is off
the cell phone or destination device is in airplane mode
the cell phone or destination device is out of funds / account suspended
the cell phone or device is roaming internationally or off-network
invalid phone number (landline, home phone or VoIP without SMS support)
recipient has blocked your number
recipient has message filtering enabled on their device (Messages from unknown/non-contacts routed to spam/junk folder (e.g., "Unknown Senders" on iPhone, filtered in Google Messages or Samsung apps), hidden notifications, or auto-deleted.)
the cell phone has insufficient memory / full storage (Device may receive the message at the network level (hence "delivered"), but can't store/display it properly due to low space.)
delivery delay due to high traffic on cell network (Messages can queue for hours/days; sender sees "delivered" early, but recipient doesn't see it until later (or never if queue expires).
message includes a suspicious link (e.g., bit.ly and goo.gl or other shortened/known spam domains)
Carrier-level spam filtering or content blocking — Even if "delivered" to the device, the carrier (or downstream filters) silently drops/quarantines messages flagged as spam, promotional, or containing prohibited content (e.g., certain links, keywords, or high-volume sending patterns).
Device malfunction or software glitch — The phone receives it at the network layer but the messaging app crashes, fails to render, or has a corrupted thread/cache (common on Android with Google Messages or older iOS versions).
Full inbox or message storage limit reached — Some older phones or carriers enforce strict limits; new messages get "delivered" but are rejected or invisible.
Do Not Disturb (DND) mode or Focus modes (especially on iPhone) — Can suppress notifications and hide messages in certain folders, making them seem unreceived (though the message is there).
RCS/Chat features mismatch or bug (Android-specific, or cross-platform with iPhone RCS support) — If RCS is enabled, messages might show "delivered" via data but fail to display properly due to RCS toggles, carrier support issues, or fallback to SMS failing silently.
SIM card issues — Faulty/damaged SIM, or SIM not properly seated, can prevent message display even if the network acknowledges delivery.
Recipient's messaging app settings — SMS reception disabled in app settings, default messaging app changed (e.g., to WhatsApp or third-party), or "Receive SMS Messages" toggled off.
False positive delivery report from carrier/API — Especially with A2P/business messaging or certain carriers; the network reports "delivered" prematurely due to infrastructure limits, but it never reaches the handset.
Message quarantined by device security/antivirus — Apps like Avast, Malwarebytes, or built-in phone security may flag and hide/quarantine texts with links/attachments.
Carrier violations:
Cell phone carriers such as T-Mobile, AT&T and Verizon filter text messages to minimize spam. Cell phone carriers use AI (artificial intelligence) to filter text messages. Here are some of the reasons that text messages may be filtered or rejected:
high opt out rates and blocking of your number by recipients
large sending volume averaging over 200 individuals per day
low reply rate - are your recipients replying to your messages?
long messages with links
unbranded shortened URLs like bit.ly, tinyurl.com
words like cannabis, CBD, gummies will cause cell phone carriers to block your texting number
Here is a list of words that could flag your number: click here
Tips to improve deliverability:
ask the patient to save your office phone number as a contact in their cell phone
ask the patient to text the word "START" to your texting number
ask the patient to check their message filtering settings
Keep messages short, clear, and free of risky elements - Limit to under 160 characters to avoid splitting. Avoid suspicious shortened links (e.g., bit.ly unless from a trusted domain), excessive punctuation, all caps, or spam-like keywords. Include sender ID (e.g., "From: Dr. Smith's Office")
Educate patients to check spam/junk/unknown folders and carrier blocks
Advise patients on device/carrier-specific fixes - Ask them to: restart their phone, ensure SMS is enabled in settings, check for full storage/low memory, disable aggressive spam filters
Limit frequency and timing - Don't overwhelm patients - stick to essential reminders (e.g., 24-48 hours before appointments) and avoid sending too many per month to prevent opt-outs or blocks.