How Many Catch-All Emails Can You Send Without Crossing Your Bounce Ceiling?

You can send to as many catch-all addresses as fit under your bounce ceiling once the valid addresses are counted, and the arithmetic takes four numbers. Most advice on catch-all addresses is a yes or no. The real question is a quantity: how many of them, in this send, given what you can tolerate. This post lays out that calculation, says where the inputs have to come from, and links the free calculator that does the sums.

Work out how many fit →

Why catch-all is a quantity question

A catch-all domain accepts mail for any address, real or not (see our glossary entry on catch-all domains and what a catch-all domain is). A mailbox check therefore cannot confirm that a given address exists. Some of those addresses are live mailboxes, and some will bounce after the server accepts the message and later reports failure, which RFC 5321 allows. The codes in a later bounce are explained in RFC 3463.

So the answer is neither "never" nor "always". Dropping every catch-all address throws away real prospects. Sending to all of them risks a bounce rate you may not be able to afford. The middle path is to include some and decide how many with a number. Our post on sending to catch-all emails covers the policy; this one covers the number.

The inputs

The calculator asks for:

1. Valid addresses: the count your verification marked valid.
2. Catch-all addresses: the count at catch-all domains.
3. Unknown addresses: the count your check could not resolve, if you want to include them.
4. Expected bounce rate for each group.
5. Your ceiling: the highest bounce rate you will accept for this send.

The first three come from a verification report, such as the valid, risky, invalid and catch-all report. The rest come from you, and they are the part that matters most.

The arithmetic

It is plain multiplication and division:

• Expected bounces for a group = the number of addresses in it times its expected rate.
• The send's bounce rate = total expected bounces divided by total addresses sent.

The valid group goes in first, since it is the safest. Each risky group then adds addresses, lowest expected rate first, until adding more would push the send's rate past your ceiling. A group whose rate is already under the ceiling fits entirely. If the valid group alone is over the ceiling, nothing risky fits.

An illustration with made-up round numbers, purely to show the mechanics and not a prediction of anything: if you had 1,000 valid addresses expected to bounce at 1%, that is 10 expected bounces. If you then added 500 catch-all addresses at an expected 10%, that is 50 more, giving 60 expected bounces from 1,500 addresses, a rate of 4%. If your ceiling were 3%, the calculator would tell you how many of the 500 fit and show the rate you would see if you sent everything. Do not copy those percentages; use your own.

Where the rates come from

From you. The calculator does not assume them, and neither should we. Three honest sources, best first:

1. Your own past sends. If you have sent to catch-all addresses before, the bounce rate of that send is the best estimate for a similar list. Pull it with bounce rate by source or the bounce rate calculator.
2. A small test send. Send to a small slice of the catch-all group first, measure, then use the result for the rest.
3. A cautious guess. If you have nothing, enter a pessimistic number and see what fits. If the answer is "nothing", you have learned something.

Note that results can differ by domain. A catch-all domain run by a large company may behave differently from one run by a small business with a default mail setup. If you can split the group, do it; the bulk catch-all checker sorts addresses by catch-all status, and catch-all scoring is covered separately on the site.

Choosing a ceiling

The ceiling is whatever your sending platform tolerates before it acts on your account, with room to spare. Platforms publish their own lines and judge over their own windows and counts, so check yours rather than copy a number. The bounce rate calculator lists the figures platforms publish. Your ceiling can also be tighter than the platform's: if one inbox is new or recently bounced, you may want more room. See the bounce budget per inbox.

Step by step

1. Verify the list. Export or note the counts of valid, catch-all and unknown.
2. Enter the counts in the calculator.
3. Enter an expected bounce rate for each group, from your own history if you can.
4. Set your ceiling.
5. Read how many risky addresses fit, and the rate you would see if you sent everything.
6. Send the valid addresses and the catch-all addresses that fit. Hold the rest.

Which catch-all addresses to include

The calculator does not pick which catch-all addresses join; any order of rows gives the same expected rate. You pick. Sensible tie-breakers that do not require made-up data:

• Prefer addresses that fit a pattern you have seen work at that company, such as one that has replied before.
• Prefer addresses at domains where your past sends bounced less.
• Put the highest-value leads first.

If you send catch-all addresses inside a sequence, catch-all leads in sequences covers how to handle the follow-ups, and Google Workspace catch-all verification covers a common case.

What it cannot tell you

• The rates are your estimates; a wrong estimate gives a wrong limit.
• It treats each group as one steady rate, which is simpler than real lists.
• It does not pick which addresses to include.
• Platforms judge bounce rates over their own windows; check yours.
• Nothing is verified or sent by the calculator; it is arithmetic in your browser, and nothing is uploaded.

Where verification fits

The calculator needs counts, and counts come from a real check. SimpleVerifier reports valid, risky and invalid results with the reason, and flags catch-all domains. Pro is $39 a month, with the first 100,000 checks a month at full speed, then slower, never cut off. See pricing, and how often to verify a list for timing.

Get the counts for your list →