Message formatting and limits

Every message you send through BlueReacher targets one of three channels: imessage, rcs, or sms. The three do not accept the same content. This page tells you what each one carries, what gets rewritten on the way down, and what to build so a single payload works on all of them.

Text

Message text goes in the content field as UTF-8. Whitespace is preserved, including line breaks (\n). There is no markdown rendering on any channel. Asterisks stay asterisks.

Length caps

Channel	Hard cap on `content`	Behavior at the cap
iMessage	20,000 characters	Request rejected with `content_too_long`
RCS	3,072 characters	Request rejected with `content_too_long`
SMS	1,600 characters	Delivered as multiple segments, billed per segment

Caps are not targets. For a first touch on a cold thread, stay between 90 and 320 characters. Past roughly 400 characters an iMessage bubble stops fitting on one screen, and reply rates on multi-screen opening messages drop hard. Save the long version for the reply.

SMS segment math

SMS is the only channel where character count costs money. The encoding your text triggers decides how many characters fit per segment.

Encoding	Single message	Per segment when split	Triggered by
GSM-7	160 chars	153 chars	Plain ASCII letters, digits, basic punctuation
UCS-2	70 chars	67 chars	Any emoji, curly quote, ellipsis character, em dash or en dash character, accented letter, non-Latin script

One curly apostrophe pasted from a doc editor cuts your SMS capacity by more than half. Strip smart punctuation before you send: replace curly quotes with straight quotes, the ellipsis character with three periods, and long dash characters with a comma or a period. In GSM-7, the characters ^ { } [ ] ~ \ | and the euro sign each count as two.

Emoji

iMessage and RCS render the full current Unicode emoji set, including skin tone and multi-person sequences. SMS renders whatever the receiving handset supports, so emoji added after roughly 2021 can land as an empty box on older Android devices. Two rules that matter operationally:

One emoji in an SMS-fallback message costs you 90 characters of capacity. Decide whether it earns that.
A skin tone modifier or a family sequence is several code points, not one character. A single such emoji can consume 7 to 11 characters of your budget.

Emoji in the content field never affect iMessage deliverability. They affect SMS cost and SMS rendering only.

Media

Attach files with media_url. BlueReacher fetches the file, stores a copy, and sends that copy. One media_url per message. To send several files, send several messages 2 to 4 seconds apart. Your media_url must:

Use HTTPS with a valid certificate
Return HTTP 200 within 10 seconds, with no authentication challenge and no redirect chain longer than two hops
Send an accurate Content-Type header (this is how the file type is detected, not the file extension)
Stay reachable for at least 60 minutes after the request if it is a signed URL

Supported types and size limits

Type	Accepted formats	API max	Delivered on iMessage	Delivered on RCS	SMS fallback
Image	JPEG, PNG, GIF, HEIC, WebP	100 MB	Up to 100 MB, original quality	Up to 10 MB, recompressed above that	Downscaled to fit 500 KB
Video	MP4 (H.264 + AAC), MOV	100 MB	Up to 100 MB	Up to 10 MB, transcoded	Replaced with a hosted link
Audio	M4A, CAF, MP3, WAV, AMR	25 MB	Up to 25 MB	Up to 10 MB	Replaced with a hosted link
Document	PDF	25 MB	Up to 25 MB	Replaced with a hosted link	Replaced with a hosted link

The practical target for anything you want to look identical on all three channels is an image under 500 KB. A 1200 x 1200 JPEG at quality 80 lands near 250 KB and fills the bubble on every device. Animated GIFs should stay under 3 MB. For video, encode H.264 baseline profile with AAC audio, keep it under 30 seconds, and keep the file under 10 MB. That clears iMessage and RCS intact and keeps the SMS link small enough to load on a weak connection.

Voice memos

To render as a playable voice memo bubble on iMessage rather than a generic file attachment, send .caf or .m4a with mono audio at 22 kHz or lower. MP3 and WAV files attach as documents and lose the waveform and the inline play button. Keep voice memos under 60 seconds. Anything past two minutes is usually not played. On RCS the same file arrives as an audio attachment with a plain play control. On SMS it becomes a link.

Links

A bare URL in content renders as a rich preview card on iMessage. The preview is built on the recipient’s device from your page’s Open Graph tags, not by BlueReacher. For the card to appear you need og:title, og:description, and an og:image under 1 MB on a page that returns 200 to an anonymous request. If your page sits behind a bot filter or a cookie wall, the card fails and the recipient sees a plain blue link. Put the URL on its own line at the end of the message. A URL in the middle of a sentence still previews, but the card pushes the rest of your copy down.

Why public URL shorteners hurt you

Do not send bit.ly, tinyurl.com, or any other shared shortener domain. Four concrete reasons:

Reputation is shared. Carrier SMS filters score the domain, not your account. Every spam campaign that used that shortener this month is part of your score.
Several public shortener domains are already on US carrier blocklists. The message is dropped silently and you are billed for it.
Each redirect hop is another chance for the preview fetch to time out. Two hops means the iMessage card usually fails to build.
Recipients cannot see the destination. A hidden destination in an unsolicited message reads as a scam, which drives the report rate that governs your line health.

Use a subdomain you control, like go.yourcompany.com, with a valid certificate and exactly one redirect. Send it on warm threads first. Never put a link in the first message of a cold thread.

What survives the fallback

When a recipient is not reachable on iMessage, the message steps down to RCS, then to SMS, based on your line settings. Content is rewritten at each step. Assume the SMS version is what a recipient will see and write the copy so it still works there.

Feature	iMessage	RCS	SMS
Plain text	Up to 20,000 chars	Up to 3,072 chars	Up to 1,600 chars, segmented
Emoji	Full support	Full support	Handset-dependent, costs capacity
Line breaks	Yes	Yes	Yes
Images	Up to 100 MB	Up to 10 MB	Downscaled to 500 KB
Animated GIF	Yes, animated	Yes, animated	First frame only
Video	Up to 100 MB inline	Up to 10 MB, transcoded	Hosted link
Voice memo bubble	Yes, with waveform	Audio file, plain player	Hosted link
PDF	Yes, inline	Hosted link	Hosted link
Link preview card	Yes	Yes	No, raw URL
Typing indicator	Yes	Yes	No
Read receipts	Yes, if recipient enables them	Yes, if recipient enables them	No
Delivery receipt	Yes	Yes	Carrier-level only
Inbound reactions	Tapbacks delivered as events	Reactions delivered as events	Text like “Liked …”
Blue bubble	Yes	No	No

Every BlueReacher line is a dedicated iMessage line, managed for you, with no A2P registration required. The fallback channels carry the same content rules described above.

Sending media

curl -X POST https://api.bluereacher.com/functions/v1/messages \
  -H "Authorization: Bearer bluereacher_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "+14155550142",
    "to": "+14155550199",
    "content": "Here is the 40 second walkthrough I mentioned.",
    "channel": "imessage",
    "media_url": "https://cdn.yourcompany.com/clips/walkthrough.mp4",
    "external_id": "seq_412_step_3"
  }'

{
  "id": "msg_01J9K2WQ7T3X0RCPB4M6ZN8VDA",
  "line_id": "line_01J8ZQ4C7B2R9YKF3H6TMXW5PN",
  "contact_id": "cnt_01J8ZR6D9F4S1MTV5J7QKXB2HC",
  "from": "+14155550142",
  "to": "+14155550199",
  "content": "Here is the 40 second walkthrough I mentioned.",
  "channel": "imessage",
  "media_url": "https://cdn.yourcompany.com/clips/walkthrough.mp4",
  "external_id": "seq_412_step_3",
  "status": "queued",
  "created_at": "2026-07-24T16:22:08Z"
}

status returns queued because media is fetched after the request returns. Watch the message webhook for sent, delivered, or failed.

Errors

HTTP	`error.code`	Cause	Fix
400	`media_url_unreachable`	Fetch returned non-200, timed out past 10s, or required auth	Serve the file over public HTTPS with no auth
415	`media_unsupported_type`	`Content-Type` is not in the supported table	Set the correct header on your file host
413	`media_too_large`	File over the API max for its type	Compress before uploading to your host
422	`content_too_long`	`content` exceeds the cap for `channel`	Shorten, or split into two messages
422	`content_required`	Both `content` and `media_url` empty	Send at least one of the two
429	`rate_limited`	Line send rate exceeded	Back off and retry using the `Retry-After` header

A failed media fetch fails the whole message. Text is not sent on its own as a partial result.

Getting started

Integrations

Platform

Message formatting and limits

Text

Length caps

SMS segment math

Emoji

Media

Supported types and size limits

Voice memos

Links

Why public URL shorteners hurt you

What survives the fallback

Sending media

Errors

​Text

​Length caps

​SMS segment math

​Emoji

​Media

​Supported types and size limits

​Voice memos

​Links

​Why public URL shorteners hurt you

​What survives the fallback

​Sending media

​Errors

Text

Length caps

SMS segment math

Emoji

Media

Supported types and size limits

Voice memos

Links

Why public URL shorteners hurt you

What survives the fallback

Sending media

Errors