Verifying Candidate and Client Emails: A Guide for Recruiters

Recruiters hold two lists that decay at different speeds. Candidate emails are mostly personal addresses that survive job changes; client emails are work addresses that die when the hiring manager moves on. Verify both before any mass mailing, but re-verify client contacts more often, and read bounce reasons rather than deleting records.

An ATS is one of the oldest databases most businesses run. Agencies keep candidates for years because the right person for a role next spring may be someone who applied for something else today. That is the right instinct for recruiting and the wrong one for email deliverability, unless you check addresses before you use them.

Two lists, two decay patterns

Candidate and client records go stale for different reasons, so treat them as separate segments. This is the main thing generic list-cleaning advice misses for recruiters.

	Candidates	Client contacts
Typical address	Personal (Gmail, Outlook, iCloud)	Work domain
Dies when	The person abandons the inbox	The person leaves the employer
Decay speed	Slow	Tied to job turnover
Common failure	Typos at application, old university or ISP addresses	Mailbox deleted after departure
Silent failure	Inbox exists, never read	Mailbox kept as a shared inbox, nobody reads it

Job turnover sets the pace for the client side. The US Bureau of Labor Statistics' January 2026 tenure survey puts median tenure with the current employer at 4.1 years across all wage and salary workers, and 20.6% of workers had been with their employer for a year or less. Tenure varies by role, which matters when you know which roles your clients hire for:

Occupation group (BLS, Jan 2026)	Median tenure
Management	6.1 years
Business and financial operations	4.6 years
Computer and mathematical	4.6 years
Sales and related	3.3 years
Service occupations	2.9 years

Source: BLS Table 6. A median is not a decay rate, and these figures do not tell you what share of your client addresses will bounce this year. They do tell you which segments to check first: a list of sales managers will go stale faster than a list of finance directors.

What your ATS does when an email bounces

ATS bounce handling records failures after the fact; it does not stop the first one. Bullhorn is the clearest example because it documents the behaviour in detail.

In Bullhorn Automation:

• A hard bounce is not retried.
• Three soft bounces are treated as a hard bounce.
• The record's mailable status becomes No (Unsubscribed By Bounce).
• If another record shares the same address, it can be marked "Unsubscribed by Bounce of Contact With Same Email".
• Bullhorn recommends keeping bounce rates below 2.5%.

There is a detail that catches people out. Bullhorn ATS and Bullhorn Automation keep separate opt-out records, and the ATS massMailOptOut field is not changed by a hard bounce. So an address that bounced in Automation can still look mailable to someone sending a mass mailing from the ATS. Updating the email address after a hard bounce resets the mailable status on the next sync, which is what you want once you have a working address.

To find bounced records, Bullhorn's guidance is to use Advanced Search on the Contacts list, choose Candidates or Sales Contacts, and filter on Has Activity = Bounce.

Other ATSs (Greenhouse, Lever, Recruit CRM, Loxo and others) handle bounces in their own ways. Check your platform's help centre for the exact behaviour, especially whether a bounce in a nurture campaign also blocks one-to-one email.

Verify before the mass mailing, not after

Run a segment through a verifier before it goes into a mass mailing or automation, then send only to valid addresses. This is the step that keeps bounce rates under Bullhorn's 2.5% guidance without waiting for bounces to tell you.

1. Build the segment in your ATS (for example, "Java developers, London, last contacted over 12 months ago").
2. Export email, record ID and record type as CSV. Keep the ID so you can match results back.
3. Verify the file. SimpleVerifier takes CSVs up to 100,000 rows; see how verification works without sending.
4. Import the results as a custom field or tag, such as email_status = invalid.
5. Send only to valid, and treat risky addresses (often catch-all domains) as a smaller, separate send.
6. Do not delete invalid records. Mark the email as bad and keep the candidate's skills, history and phone number.

The last point matters more in recruiting than almost anywhere else. A candidate's record has value well beyond the email address. A dead address is a reason to call or message on LinkedIn, not to throw away the profile.

Client contacts: the address that dies with the job

When a client's hiring manager leaves, their work address usually stops accepting mail, but not always straight away. That timing affects what a verifier can tell you.

Two common setups at client companies:

• Google Workspace: an admin can restore a deleted user for up to 20 days, and Google suggests suspending rather than deleting in some cases (Google Workspace admin help).
• Microsoft 365: a deleted mailbox is kept in a soft-deleted state for 30 days (Microsoft Learn). Many organisations instead convert a departed employee's mailbox to a shared mailbox, which needs no licence under 50 GB (Microsoft Learn).

The second case is the awkward one. A former hiring manager's address converted to a shared mailbox still exists, so a verifier correctly reports it as valid. The address works; the person is gone. Verification cannot detect that. Only replies, or the lack of them, can.

So for client contacts:

• Verify to catch the addresses that have been deleted.
• Watch for silence on addresses that verify as valid but have not replied in months. Check LinkedIn before the next business development email.
• Find the replacement. When a hiring manager has moved on, the role usually still exists. Use the company's email pattern to find their successor; company email formats explains how, and our email finder checks the guess for you.

Bullhorn publishes a workflow for exactly this. Its Herefish client bounce automation looks for client contacts with a hard bounce in the last 7 days, sends a daily alert to the contact's owner, and has the owner phone or text the client to get the right address. It is manual, and it is the right instinct: a bounced client is a relationship problem first and a data problem second.

Candidate addresses: typos and abandoned inboxes

Candidate addresses fail mostly at entry, through typos, and later through abandonment. Two habits catch most of it:

• Check at application. Typos like gmial.com or a missing letter in a long surname are common on mobile application forms. A real-time check on the form, or a nightly verification of new applicants, catches them while the candidate is still engaged. See real-time verification on forms.
• Watch old student and ISP addresses. Candidates who applied years ago with a university address may have lost it on graduation. These show up as invalid when verified, and are worth replacing rather than retrying.

Data protection and old candidate records

Keeping candidates for future roles is normal, but in the UK and EU you need a reason to keep the data and must tell candidates you are doing it. This is not legal advice.

The UK GDPR's storage limitation principle says personal data must not be kept longer than necessary. The ICO's older Employment Practices Code advised employers that keep unsuccessful applicants on file for future vacancies to tell them so and give them the chance to have their details removed.

Verification and retention meet in one place: a record whose email has been invalid for years and who cannot be reached any other way is a candidate for deletion under your retention policy, not just a deliverability problem.

A verification schedule for a recruitment database

Check new records on entry, segments before every campaign, and client contacts more often than candidates.

When	What	Action on invalid
On application or record creation	New candidate and contact emails	Ask for a correction while they are engaged
Before each mass mailing or nurture	The segment being sent	Exclude; mark email bad
Quarterly	Active client contacts	Find the replacement contact
Annually	Whole database	Review against retention policy

The takeaway: in an ATS the client list is the one that rots, because it is tied to job changes. Verify client contacts more often than candidates, keep the records when the email dies, and treat a bounced hiring manager as a prompt to find who replaced them.