From, Reply-To and Sender display names, the subject, and supported plain-text and HTML bodies.
Set account variables
1
Open the account
Open Accounts and edit a sending account. For the managed Amazon SES account, select Edit variables from its menu.
2
Add a key and value
In Variables, add
signature_url with the URL for that account. Select Save variables.3
Use the tag
Insert
[DP_VAR_SIGNATURE_URL] into your email template. Send a test message and inspect its delivered content and selected provider in Logs.Key and value limits
Each account can store at most 50 keys. Keys contain 1–64 ASCII characters and must match^[a-z][a-z0-9]*(?:_[a-z0-9]+)*$. Start with a lowercase letter; use lowercase letters, digits, and single underscores between nonempty segments. Leading, trailing, and repeated underscores are invalid.
Each value is a string of at most 4,096 Unicode code points. An empty string is valid. To form a tag, uppercase the key and add the DP_VAR_ prefix inside brackets: signature_url becomes [DP_VAR_SIGNATURE_URL].
Substitution rules
Valid custom tags whose keys are unset become empty strings. Values do not expand template tags inside another value. Body values are inserted raw: Sendmux does not escape HTML or encode URLs. Prepare each value for the context where you insert it. Subject substitutions remove control characters so a value cannot inject another email header. Body values retain their original content. Substitution supports plain text, HTML, quoted-printable, and base64 message content, including encoded subjects.Display names
Built-in[DP_*] and custom [DP_VAR_*] tags work in the display names of From, Reply-To and Sender, including encoded names. Literal text around each tag is preserved. These names also support substitution when the message has no subject.
For example, use the selected account’s configured From name:
Sender has no default. Substitution preserves each address, its order and any address group. Existing sender address routing and explicit Reply-To address overrides still apply. A default Reply-To name alone does not collapse a list of reply addresses.
Excluded locations
Template substitution does not change any address component or any other header, includingTo, Cc, Bcc, Message-ID, Date, Received, DKIM-Signature, List-*, Content-*, X-Sendmux-* and custom X-* headers.
These restrictions protect recipient addresses, routing metadata, identifiers and security fields. Excluded means no template substitution; existing header stripping and rewriting still apply.
Sendmux does not substitute template tags inside attachments, signed or encrypted message parts, or attached emails.
Variables belong to the selected provider, not the recipient or credential. Passwords, access tokens, and other connection secrets have no built-in template tags.
Built-in tags
These seven tags read the selected provider’s configured values:
The sender-related tags read provider settings. An unset setting does not fall back to the sender supplied in your message.
Edit several accounts
Select accounts in Accounts, then open Update Variables and choose a mode:
When Replace all has no keys, select Confirm clear to remove all variables from the selected accounts, or Cancel clear to leave them unchanged.
Select Apply changes to start the update. Limits apply to each resulting
map, including keys already on the account. Review the reported failures after
a bulk edit, then open an affected account to verify its values.
Management API
The provider detail response includesvariables, returning {} when unset. Include the optional map when creating a provider or updating it with PATCH /providers/{public_id}:
variables from a PATCH preserves the existing map. Supplying it replaces the map, and { "variables": {} } clears all keys. Provider list and delivery-group summaries omit variable values; fetch the provider detail when you need them.
Related guides
Delivery groups
Restrict a message to providers in selected groups.
Sending accounts
Configure the providers that supply template values.