Two questions hide inside "is this email still active". One is whether the mailbox exists and takes mail today. The other is whether anyone opens it. A verification check answers the first in seconds. No protocol answers the second, for any tool.
Here's how the existence check works. Your verifier looks up the domain's MX record, connects on port 25 and names the address at the RCPT TO step. A 250 reply means the server accepts it, and a 550 means no such user. The connection closes before DATA, so no email is sent and the owner never sees a thing.
Activity needs your own data. Look for a reply, an open or a click in recent months, which your ESP or sequencer stores per contact. When an address passes verification but hasn't engaged in a year, move it to a re-engagement send and keep it off your main list.
Addresses drift between the two states faster than most people expect. Hunter tracked verified addresses for eight weeks and found 5.5% had degraded: 2.3% turned invalid and 3.2% became accept-all (Hunter, 4 November 2025). A check from last quarter isn't a check for this week's send. Our page on how often to clean a list sets out a schedule.
To check one address, paste it into the free email verifier. For a whole list, upload a CSV to bulk verification. ZapBounce returns valid, invalid, catch_all or unknown for every row, keeps your original columns, and charges $5 for 1,000 checks. Unknown results and duplicates cost nothing.
Related questions
Can you tell if someone still reads their email?
No verifier can, because a mail server answers for the mailbox and never for the reader. Replies, opens and clicks in your own sending tool are the signal that a person is behind it. Use a verification check for existence and your engagement data for activity.
How do I check if a Gmail account is still active?
Run the address through an email verifier. Gmail rejects a deleted or nonexistent address with a 550 code at the RCPT TO step, so the row comes back invalid. When the server declines to answer the probe, ZapBounce returns unknown and bills nothing.
Does checking if an email is active notify the owner?
No. The check ends before the DATA step, so no message reaches the inbox. The owner has nothing to open, read or reply to.
How often should I recheck an old list?
Recheck any list you haven't mailed in two months before the next send. Hunter measured 5.5% of verified addresses degrading within eight weeks in its November 2025 study.