The number of times a trigger can fire depends on the number of records that are processed and the number of DML operations that are performed. Some operations can cause the trigger to fire multiple times, either by updating the same records or by updating related records. These operations include:
* Process Flows: A process flow is a declarative tool that can automate complex business processes by executing actions based on criteria. A process flow can update the same record that triggered it, or a related record, which can cause the trigger to fire again1.
* Workflow Rules: A workflow rule is a declarative tool that can automate tasks and field updates based on criteria. A workflow rule can update the same record that triggered it, or a related record, which can cause the trigger to fire again2.
* Roll-Up Summary fields: A roll-up summary field is a custom field that aggregates child record information into a parent record. A roll-up summary field can update the parent record when a child record is inserted, updated, deleted, or undeleted, which can cause the trigger to fire again3.
The other options do not affect the number of times a trigger can fire. Criteria-based sharing calculations and email messages do not update records or cause DML operations. References:
* Process Automation | Salesforce Help
* Workflow Rules | Salesforce Help
* Roll-Up Summary Fields | Salesforce Help