Ah, invalid email addresses… those contacts you think are good, but who, in reality, will never receive your messages. For e-marketing experts, they represent a major obstacle. Hardly visible, they gradually undermine deliverability, skew indicators, and damage sender reputation. This is why it is important to understand them, differentiate them, and know how to handle them.
My address is “invalid”: what exactly does that mean?
An invalid email address is simply an address that cannot receive messages. In other words, even if it sometimes looks like a real address, sending it fails for several reasons.
The different types of errors encountered for invalid addresses
1) The address does not follow the correct syntax (absence of “@”, non-existent domain, etc.). The message therefore cannot be sent.
Common examples:
prenom.nom@domaine → .com / .fr is missing
prenom@nom@domaine.com → multiple @
prenom.nom@domaine,com → comma instead of a dot
prenom@.com → empty domain part
2) The domain of the address does not exist or has no valid records. The email is rejected upon verification by the recipient server.
Possible causes:
- There is a typo in the domain name (gmial.com, hotmial.fr, etc.)
- The domain is deleted or expired.
- No mail server.
- The domain is temporarily inaccessible.
3) The domain exists, but the mailbox does not (or no longer) exist. A code like “550 5.1.1 User unknown” or “550 5.1.0 Address rejected” is displayed. Here the failure is definitive, and the address must be immediately removed.
Possible causes:
- The user has deleted their account (job change, deactivated personal address, etc.).
- The address was entered incorrectly originally.
- The account is blocked or suspended.
4) The server temporarily refuses the message but may accept it later. A code like “452 4.2.2 Mailbox full” or “421 4.4.0 Temporary failure” is displayed. Therefore, the message is not delivered instantly but could be later.
Possible causes:
- The mailbox is full.
- The recipient server temporarily unavailable.
- The message is too large.
- The sending quota or limit has been exceeded.
5) Some addresses are not invalid per se but are rejected for security reasons. The email bounces or is filtered without being read.
Possible causes:
- SPF / DKIM / DMARC are misconfigured so your sending server is rejected.
- The domain requires a second attempt before accepting (greylisting).
- The address exists, but your message is rejected due to an anti-spam block.
- The domain accepts everything in SMTP and then filters in case of a potential trap.
Why invalid addresses harm performance and compliance
Reputation and inbox placement
A lot of hard bounces is a strong signal to ISPs that your database is poorly maintained. It’s very bad for your sender reputation first and foremost and, in the long term, for the placement of your emails in mailboxes. You risk ending up in Promotions tabs at best, and in spam at worst.
It is therefore more than recommended to quickly eliminate these addresses and closely monitor server feedback.
The real marketing cost
An invalid address also represents a certain cost: it inflates volumes without revenue potential, it skews your indicators (open rate, CTR), and wastes your time (so money).
Compliance
The GDPR imposes the “principle of accuracy” for personal data. These must not only be accurate and up-to-date, but inaccuracies must also be “erased or rectified without delay” (art. 5).
For emails, this means that keeping invalid addresses without a correction/deletion mechanism goes against this principle and exposes the sender to sanctions.
What to do with invalid addresses?
Identify the type of invalidity
As mentioned above, not all invalid addresses are the same. Before taking action, you need to know why they are invalid. Identifying the cause of the problem will allow you to distinguish what can be corrected from what needs to be removed.
Clean methodically
Start by removing hard bounces; addresses confirmed as invalid must be permanently removed from your lists. Continuing to send emails to them will only bring you trouble, so there’s no point in persisting.
Place soft bounces in quarantine as they are often temporary. Retry sending over two to three successive campaigns. If the problem persists, you can then disable the address.
Some errors are recoverable, like a simple typo for example. This means that the affected addresses can be corrected rather than deleted. Consider using a correction suggestion system, but never modify automatically without user validation.
Punctual cleaning is not enough. It is essential to establish a continuous verification process to maintain the hygiene of your lists. This includes sign-up validation, double opt-in, as well as automated monitoring of bounces in your ESP.
The good news? Invalid addresses are not inevitable, and you can definitely regain control over the quality of your data by following these tips. It’s a long-term job, of course, but it brings more deliverability, less waste, and better relationship quality. In short, everything you need to get into and stay in the inbox!
