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POST
Send a Fax

Authorizations

Authorization
string
header
required

API key as Bearer token. Use an account key (mfx_acct_...) for /account/* endpoints, and an environment key (mfx_test_... for sandbox, mfx_live_... for live) for /environment/*, /faxes, /webhooks, and /events.

Headers

Idempotency-Key
string

Client-generated key for idempotent submission (recommended). Duplicate keys return the original response without re-processing. Keys expire after 24 hours.

Body

multipart/form-data
to
string
required
Pattern: ^\+[1-9]\d{1,14}$
file
file
required
Maximum string length: 10240
webhook_url
string<uri> | null
Maximum string length: 2048
max_attempts
integer | null
Required range: 1 <= x <= 5
csid
string | null
Maximum string length: 20
page_size
enum<string> | null
Available options:
letter,
legal,
a4,
b4
resolution
enum<string> | null
Available options:
standard,
fine
optimize_for
enum<string> | null
Available options:
text,
photo
tags
string[] | null
Maximum array length: 10
Maximum string length: 255

Response

FaxSubmissionResource

id
string
required

Unique fax identifier (fax_-prefixed).

Example:

"fax_8aZqRm4yT3vK7pNxJ2bH9c"

status
enum<string>
required

Initial fax status.

Available options:
queued,
submitted,
in_progress,
delivered,
failed
Example:

"queued"

to
string | null
required

Destination fax number in E.164 format.

Example:

"+12125551234"

tags
object
required

Echo of caller-supplied metadata. Empty serializes as {}.

created_at
string<date-time>
required

UTC timestamp when the fax record was created.

resent_from
string

Original fax identifier when this submission is a resend; only present on resends.

Example:

"fax_8aZqRm4yT3vK7pNxJ2bH9c"

Last modified on May 11, 2026