How to build a contact list that updates itself

Set the filters once and the list maintains itself forever. The filter builder, AND vs OR, and the filters worth knowing.

If you rebuild the same list every Monday morning, you are doing a job the database should be doing. A dynamic segment stores the filters instead of the contacts, so membership is worked out fresh from your live data every time anyone opens it.

Build one

Open Segments and choose New segment The first screen asks what type you want. Pick Dynamic for a list driven by filters.
Name it after the question "No activity in 30 days" tells the next person what the list means. "Q3 push" does not, and in November nobody will remember.
Add your first filter Choose a property, an operator, and a value. Each filter narrows the list further.
Choose AND or OR AND means every filter must match. OR means any one of them is enough. This single toggle is the difference between a list of eight and a list of eight thousand.
Check the count before you save The matched count is your sanity check. A number far from what you expected means a filter is doing something other than what you read it as.

AND vs OR, the part people get wrong

Read your filters out loud as a sentence. With AND, the sentence is "contacts who are in tech *and* in the US *and* warm". With OR it becomes "contacts who are in tech *or* in the US *or* warm", which is nearly everyone you have.

Identical filters. One toggle. A list of eight, or a list of eight thousand.

The useful rule: AND narrows, OR widens. If your list came back far bigger than you expected, you almost certainly have an OR where you meant an AND.

Filters worth knowing

Health status is the workhorse. It is how you separate people worth emailing from addresses that will hurt your domain.
Last activity turns a pile of contacts into a follow-up queue. Anything past thirty days is a re-engagement list.
Company attributes let one segment cover a whole market slice without naming a single account.
Owner matters the moment more than one person sells. Without it, every rep works the same list.

Keeping it honest over time

A dynamic segment cannot go stale, but it can go wrong quietly. The usual cause is a filter on a field that stopped being filled in, which produces a list that shrinks month over month while looking perfectly healthy.

Glance at the matched count when you open a segment you have not used in a while. A number that has moved a long way with no explanation is worth two minutes.

Do

Start with one filter and add the second only after you have looked at the count.
Say the filter set out loud as a sentence before saving it.
Exclude bad addresses with a health filter on any list you intend to email.
Add an owner filter as soon as a second person joins the team.

Don't

Do not build a segment with six filters in one sitting. You will not be able to tell which one is wrong.
Do not leave OR selected by accident. It is the single most common cause of a list that is far too big.
Do not filter on a field your team does not reliably fill in.
Do not use a segment as a to-do list. Segments describe people, not your intentions toward them.

How often does a dynamic segment refresh?

There is no refresh job. Membership is resolved at read time, so it is current every time the segment is opened or used.

Can I add one contact to a dynamic segment by hand?

No, and that is the point. If a contact should be in the list, the filters should say so. If you need hand-picked membership, you want a static list.

What happens to a sequence when someone leaves the segment?

Enrollment is separate from membership. Someone already enrolled continues unless you remove them, which stops a half-finished sequence from cutting off mid-thread.