You can select the audience from a list of dynamic segments or static lists that you have created in advance. Please refer to the Audience article to get more information about creating dynamic segments and static lists.
You can select only one Dynamic segment as the target audience; however, you can select up to five different static lists as the target audience for a campaign.
Sender ID is the email address (in case of email campaign) or SMS Sender Id (in case of SMS campaign).
Refer to Communication Sender IDs article to get more information about setting up different sender IDs for communication purposes.
In the case of SMS campaign, the available list of sender IDs depend on the target audience because SMS Sender IDs have to be setup with “Local” telecom providers and different countries have different rules for setting up SMS Sender IDs. Some countries allow sender IDs to be alphanumeric like MyBrand while other countries they only allow numeric sender IDs like 12345.
For example, if your target audience include customers from Country A that allows Sender ID MyBrand then you will be able to select MyBrand as sender ID. While if your target audience includes Sender ID 12345 then you will be able to select only 12345 as sender ID.
It is always recommended to setup at least one sender ID that is common to all your countries of operation in case you want to target your global audience across different countries in one campaign. Please refer to Communication Sender IDs article.