Lead Generation Guide
Verifying a lead list before outreach: what the checks do and do not promise
Verification tells you a mail server accepted an address today. The checks that decide whether a list is any good happen earlier, in the targeting.
01
How do you verify email addresses before outreach?
To verify email addresses before outreach, run every address through an email verification check, remove the ones that come back invalid, set catch-all and unknown results aside in their own group, and check the list again shortly before you send. That protects your sending domain from bounces. It does not tell you whether the person is the right one, whether they still work there, or whether you should be writing to them at all. Those checks happen before verification, in the targeting, and they matter more. This guide explains what a verification check actually tests, what it cannot tell you, how to treat catch-all domains and generic inboxes, and how often to check a list again. It ends with a pre send checklist in three parts, with what each check can and cannot promise written beside it.
Verification is the second of three stages, not the only one. The order I work in for every list is this:
Targeting first. Decide who belongs on the list and check each contact against that decision before an address is even looked up.
Verification second. Check each address with a verification tool and sort the results into deliverable, invalid, catch-all and unknown.
The day before sending third. Check the list again against your do not email list, your earlier bounces and any changes since it was built.
A list that passes all three is a list you can send to with a clear conscience. A list that only passes the middle stage is a list of real inboxes, which is not the same thing as a list of the right people.
02
What does an email verification check actually test?
A verification tool does not send an email. It asks a series of questions about the address and the server behind it, and stops at the first one that fails.
Syntax. Is the address written correctly, with one @ sign, a valid domain and no characters that are not allowed?
Domain. Does the domain exist, and does it publish mail exchange records, which tell other servers where to deliver its email? A domain with no mail server cannot receive anything.
Mailbox. The tool opens a conversation with the receiving mail server and asks, in the language mail servers use, whether it will accept mail for this address. A clear refusal means the address is invalid. A clear acceptance means the server said yes today.
Type. Is the address a generic inbox such as info@ or sales@, a disposable address, or a domain known for temporary sign ups?
The result is a status, and each status means something specific:
Deliverable or valid. The server accepted the address when asked.
Invalid. The domain does not exist, has no mail server, or the server refused the address. Remove it.
Catch-all or accept all. The server says yes to every address on the domain, real or not, so the check proves nothing about this mailbox.
Unknown. The server did not give a usable answer, often because it was slow, busy or deliberately vague.
The standard that defines how mail servers talk to each other, RFC 5321, allows a server to decline to confirm whether an address exists, and asks that a server which declines must not appear to have verified an address it has not. That is why some results come back unknown however good the tool is.
03
What can verification not tell you?
A verified address is an address that a mail server accepted on the day it was checked. That is all it is. It cannot tell you any of these things:
Whether the message will arrive in the inbox. Acceptance at the door is not inbox placement. The same standard notes that a server can accept a message and report a delivery failure later. Spam filtering, your domain's reputation and your sending behaviour all decide where the email lands.
Whether the person is the right one. A verified address for someone in the wrong role, at the wrong size of business or in the wrong country is a wasted send, and sometimes an annoyed reader.
Whether they still work there. People change jobs. An address can stay live for weeks after someone leaves, forwarded to a colleague or collected by a shared inbox nobody reads.
Whether they read that inbox. Some addresses are live and ignored.
Whether you may write to them. Verification is a technical check. It says nothing about the rules for marketing email in Ireland or the UK, or about whether the address came from a source you can stand behind.
So a list with every address verified can still be a poor list. The work that makes a list good happens earlier.
04
What should be checked before verification, in the targeting?
This is the stage that decides whether a list is worth sending to, and it costs nothing but care. Before I look up a single address, I agree these with the client in writing:
The ideal client. Industry, location, company size and the job titles of the people who can say yes.
Who to leave out. Existing clients, competitors, companies already in conversation, and anyone on a do not contact list.
The reason to write. If there is no plain reason this business would want to hear from you, verification will not save the email.
Then each contact is checked against that agreement:
Is the business a real, trading business that matches the agreed industry, location and size?
Is this person in the agreed role at that business today, based on a current public source such as the company website or their professional profile?
Is this the person who decides, or someone who would only forward the email?
Is the address a business address for this person, not a personal one?
Can you say where the contact came from? If you cannot name the source, the contact does not go on the list.
The last check matters for more than tidiness. In the UK, the Information Commissioner's Office guidance on the accuracy principle says you must take reasonable steps to make sure the personal data you hold is not incorrect or misleading, and to correct or erase it when it is. The same accuracy principle is one of the core principles of the GDPR, which applies in Ireland. A business email address with a person's name on it is personal data. This is not legal advice, but a list with a recorded source for every contact is a list you can correct when someone tells you it is wrong.
For the rules on sending marketing email itself, see my guides to cold email in Ireland and to PECR in the UK.
05
How do catch-all domains and generic inboxes change the plan?
Catch-all domains. A catch-all domain accepts mail for any address, so verification cannot tell a real mailbox from one that does not exist. Plenty of real businesses set their domains up this way, so deleting every catch-all result throws away good contacts. Sending to all of them at once risks a burst of bounces later. The middle path is the one I use:
Keep catch-all contacts in their own group, separate from the deliverable ones.
Check the person more carefully: confirm the name, role and the address pattern the company uses elsewhere.
Send to that group in small batches, after the deliverable group, and watch the bounces closely.
Stop sending to the group if bounces start to climb, and remove every address that bounces.
Generic inboxes. Addresses such as info@, sales@ and hello@ are not people. RFC 2142 lists common mailbox names like these and ties them to business functions rather than individuals. They are often shared, filtered or tied to an autoresponder. For one to one outreach to a decision-maker, a generic inbox is a weak substitute: nobody is accountable for reading it, and a reply is rare. I leave generic inboxes off a decision-maker list unless the client asks for them, and when they are included they are marked as generic so they can be written to differently or not at all.
06
How often should a list be verified again?
A verified list is a snapshot. People leave, mailboxes close and domains change hands, so a result that was true when the list was built becomes less true every week after. There is no single correct interval, so these are the working rules I follow rather than a published standard:
Before the first send, if more than a week or two has passed since the list was verified.
Before every reuse, when an old list is picked up for a new campaign, check it again in full.
After any bounce, remove the address and look again at other contacts from the same source.
When a domain bounces more than once, check every remaining contact on that domain before writing to them.
Re-checking costs a little. Sending an old list unchecked costs your domain's reputation, which is far slower to repair.
07
The pre send checklist, in three parts
Each check is written beside what it can promise and what it cannot. Run the parts in order.
Part one: targeting, before any address is looked up.
The ideal client and the exclusions are agreed in writing. Can promise: everyone on the list was chosen for the same reason. Cannot promise: that the reason is a good one. That is your judgement.
Each business is real, trading and in scope. Can promise: no wasted sends to closed or irrelevant firms. Cannot promise: that they need what you offer today.
Each person holds the agreed role, checked against a current public source. Can promise: you are writing to the right job title. Cannot promise: that they have not moved on since the source was updated.
Each contact has a recorded source. Can promise: you can show where any contact came from and correct it. Cannot promise: that the source was accurate.
Part two: verification.
Every address has been checked by a verification tool. Can promise: the server accepted the address on that day. Cannot promise: inbox placement, a reader or a reply.
Invalid addresses are removed. Can promise: fewer hard bounces. Cannot promise: zero bounces.
Catch-all and unknown results sit in their own group. Can promise: you choose how much risk to take with them. Cannot promise: which of them are real.
Generic inboxes are removed or marked. Can promise: a decision-maker list made of people. Cannot promise: that a named address is read more often.
Part three: the day before sending.
- The list has been checked against your do not email list. Can promise: nobody who opted out is written to again. Cannot promise: anything about people who opted out somewhere you did not record it.
- Earlier bounces have been removed. Can promise: you do not hit the same dead address twice. Cannot promise: that no new address has died.
- The list is re-verified if it is more than a week or two old. Can promise: the snapshot is recent. Cannot promise: that it is still true next month.
- Your sending domain is authenticated and warmed up. Can promise: the basics a mailbox provider looks for are in place. Cannot promise: inbox placement, which depends on your content and behaviour too.
08
Frequently asked questions
Is a verified address guaranteed to deliver? No. Verification means the receiving server accepted the address when it was checked. The message can still bounce later, land in spam, or reach a person who has left. A verified list lowers your bounce risk. It does not remove it.
What is a catch-all domain? A domain whose mail server accepts email for any address on it, whether or not a real mailbox exists. Verification cannot confirm individual addresses on such a domain, so results come back as catch-all rather than deliverable. Keep them in a separate group and send to them carefully.
Should I remove generic inboxes from a list? For outreach to a named decision-maker, yes, or at least mark them. Addresses such as info@ and sales@ belong to a business function, not a person, and are often filtered or shared. Keep one only when there is no named contact and the client has asked for it.
How long does a verified list stay accurate? It starts going out of date the day it is verified. My working rule is to re-check before the first send if more than a week or two has passed, and to re-check in full before any reuse. There is no published standard for the interval.
09
When a managed service makes sense
If you want a list built this way, with the targeting agreed in writing first and every address checked, that is what my Lead Generation service does. I research the businesses, find the decision-maker in each, verify every address and deliver a spreadsheet that shows where each contact was found and whether its email was verified. It costs €0.09 per verified lead, with a minimum order of 1,000 leads (€90), half upfront and half on delivery (the pricing page, read 2026-10-24). The first list usually arrives five to seven working days after the targeting is confirmed. Verification on that list makes the same promise as any other: the address was accepted when it was checked, and nothing more. For the wider picture, start with my guide to building a useful B2B prospect list, and if you plan to send to the list yourself, my B2B Email Outreach service covers the writing and the sending.
If you would like a list built for your business, send a short written brief through the contact page and I will reply in writing.
10
Sources
- RFC 5321, Simple Mail Transfer Protocol, from the RFC Editor (opens in a new tab) — checked 2026-10-24
- The accuracy principle, guidance from the Information Commissioner's Office (opens in a new tab) — checked 2026-10-24
- RFC 2142, Mailbox names for common services, roles and functions, from the RFC Editor (opens in a new tab) — checked 2026-10-24