Signature 365 can change the signature based on the data used when composing an email in Outlook. To best demonstrate this functionality, consider mailbox john.doe@brandyouremail.io has access to another mailbox support@brandyouremail.io (the concept is the same regardless if using a shared mailbox or another user's mailbox).
Rule Configuration
Consider how you wish the rule to be applied:
- Defining the data used in the signature.
Within the rule configuration, the following checkbox is used to determine the data used. (In our example the Sender is john.doe@, and the From address is support@).
This checkbox alone is used to determine what information will be included in the signature template.
In this scenario, you wish to include a different signature depending on the mail being sent from the johndoe@ address vs from the support@ mailbox.
Depending on the configuration users may receive different signature templates; for this example, we wish to ensure when sending from the support mailbox all users are given their normal template.
In this example a rule called "John Doe Signatures" has been configured to specifically target the user with the following configuration:
Note the Match rule on Sender instead of From when email is sent on behalf of option; this determines if the rule should be triggered based on the sender or from address. In this case the rule will trigger based on the sender as a different template should be applied when sending from the support mailbox.
- Defining the matched user on a rule
A second rule exists with a similar configuration targeting the support mailbox. This rule should be matched when the From address is support@, the rule is configured with Match rule on Sender instead of From when email is sent on behalf of unchecked. 
Rule Order
You will also need to consider the ordering of these rules. Rules are always applied in priority order, and the highest priority rule will be set as the default signature. In the example, the rules are configured as follows:
For this example, Outlook has been configured using the johndoe@ account. When sending an email on behalf of the support@ email account, johndoe@ will always match the first rule, and as a result, the Support Mailbox signature will not be applied as the Sender is always the johndoe@ account.
To resolve this you must move the rules to ensure the Support mailbox rule is a higher priority.
The following order will provide the desired result since you wish to ensure everyone sending from the support mailbox receives the same template and configuration.
Overriding data in Signature Templates
When sending emails from a generic mailbox such as a support mailbox. You may wish to ensure the vast majority of information uses data from the generic mailbox (support@ in this example) but in some cases you may want to include the Sender user's data.
Within the Signature template, you can prefix any field with Sender. to force the sender mailbox information, or From. to force the from mailbox information. Below is an example template:
In the example above the FullName field is prefixed with Sender. to ensure the signature is generated with the senders full name. As this rule applied to the support@ mailbox is configured to use the From data, any field without the sender. prefix will use data of the From mailbox.
As an example, the following 2 signatures demonstrate how this will display for the johndoe@ vs the support: Mailboxes:
Signature template for John Doe:
Signature template for the support mailbox with the fullname being pulled from the Sender details.
