Are there any limitations when working with multi-select pick lists?

Multi-select picklists can be challenging to support, as they have many limitations in both Salesforce and Campaign Monitor.

The Solution

Field creation — when we create a Campaign Monitor field from a Salesforce multiselect picklist, it is created as a text field with values stored as semicolon-separated values. If you need a Select Many field in Campaign Monitor, create the field directly in Campaign Monitor first, then run the primary sync to pull it into the app before mapping it.
Default values cannot be set on multiselect picklist fields. See Are all field types supported when working with default values?
Blank values — the Campaign Monitor API does not return a response for a multi-select field when no values are selected, so blank values cannot clear or update a mapped field. See Can I clear all values from a pick list in Campaign Monitor and sync to Salesforce?
Keeping values in sync — we do not automatically update Campaign Monitor when Salesforce multiselect picklist values change. You need to keep the options in both systems in sync manually. If a value in Campaign Monitor doesn’t match its Salesforce counterpart exactly, the sync will fail for that record. We will attempt to log an error in the Maintenance section of your Settings page when a mismatch is detected.

Where possible, we recommend using single-select picklists or checkboxes instead, as these are better supported across both platforms.