There could be legitimate duplicate Contacts in ROI with the same Email addresses.
By default, ROI deduplicates contacts based on their Contact.ID.
ROI has an optional feature that can be turned on to deduplicate on Contact Email Address when a Tactic sends your Email.
Utilizing this in your account results in seeing a higher number in your Segments than in your Tactics because the Tactic isn’t being sent to duplicate Email addresses.
Please contact Support if you would like the deduplicate by Email address feature turned on in your account, or if you would like assistance cleaning up duplicate Email addresses in your Contacts.
If any of your Contacts have a blank Email address or an invalid Email address (due to a typo, a defunct account, etc.), your Segment counts will be higher than your Tactic Send.
For a more realistic Segment result count to forecast your expected Send count, add an Exclusion containing Contacts where either the Email address is blank, the Email address doesn't contain an @ symbol, or the Email address doesn't contain a . symbol.
Please read this article on Segments if you would like more information about using the Exclusion feature.
Your Segment could have a one-to-many relationship. In a one-to-many relationship, each row in your primary Table can be related to more than one row in the relating Table.
Examples of one-to-many relationships are Contacts with Events, Contacts with Purchases, Contacts at Companies with Opportunities, etc.
If a Contact a one-to-many relationship with your joining Table(s), the Contact will show up in your Segment more than once, making your Segment results higher than the distinct count of Contacts that meet your Segment criteria for the Send.
This is frequently mistaken as the Contact being duplicated on the Contacts Table.
For a more realistic Segment result count to forecast your expected Send count, use the Show Distinct Values function on one to many Segments.
Please read this article on Segments if you would like more information about using the Show Distinct Values function.
Contacts in your Segment may have previously Bounced, Unsubscribed, or marked your Email as Spam.
Tactics automatically suppress these records from your Sends, Segments do not suppress these records from result counts.
Contacts in your Segment may also Bounce, Unsubscribe, or mark your Email as Spam on this send.
For a more realistic count in Segments that will match the numbers in the Tactic Send, create and apply an Exclusion Segment to your Segment to exclude Contacts which had previously a Hard Bounce, Unsubscribed, or marked your Email as Spam.
Please read this article on Email Bounce Codes & Categories, along with this article on using the Event Types and Additional Info Strings, if you would like more information on creating an Exclusion Segment for Hard Bounces, Unsubscribes, and Spam.
If your Tactic has been previously Sent, the checkbox will determine whether Contacts are included in a repeat Send of the same Tactic.
By default, the Include any Contacts that were already a part of this Tactic box is unchecked; however, it may be checked if you would like an Email to send to the same address more than once.
If the box is unchecked, the repeat Send count could be smaller than the Segment, based on any Contacts that were previously sent in the Tactic.
Please read this article on how to Send an ROI Email, if you would like more information about this check box.