How to find malformed email addresses in a CSV

A contact CSV can look fine at a glance and still contain addresses with a missing symbol, an extra space, or a typo in the domain. Those small errors can cause messages to bounce or make a contact hard to reach.

Use the CSV Editor to open the file in your browser, find suspicious entries, and make careful corrections. It can help you inspect and edit rows, but it cannot prove that an address exists or that its owner can receive mail.

Find suspicious email entries

1. Open the CSV Editor and load your contact CSV. The file is opened in your browser, so you can inspect it without uploading it to a website.
2. Find the column that contains email addresses. Check the header and a few rows to make sure you have the right field, especially if the file has columns such as Work email, Personal email, or Alternate email.
3. Look through the entries for obvious problems. Common examples include sam.example.com with no at sign, sam@@example.com with two, or sam@ with no domain after the at sign.
4. Use the editor's Find feature to locate visible problem characters or fragments, such as a space or repeated at signs. Check each match in its row before changing anything, since the same character may appear in another column.
5. Edit only entries you can correct confidently. Then inspect the changed rows and save or export the edited CSV using the file option available in the editor.

Keep the original file unchanged until you have checked the edited copy. If you are reviewing a large list, work in smaller groups or note the row numbers of entries that need confirmation. That makes it easier to return to uncertain cases instead of guessing.

What the entries may tell you

The address has no at sign, or more than one

A typical email address has one at sign separating the mailbox name from the domain, as in sam@example.com. If it is missing or repeated, the entry is probably incomplete or mistyped. Do not add or remove characters unless another trusted source, such as the contact's original form, shows what the address should be.

The domain is missing or looks incomplete

In a typical public email address, the part after the at sign has a domain name and an ending such as .com or .org. An entry like sam@example may be incomplete. A missing period is a useful warning sign, but it is not a complete test of every possible email system. Check the contact's source rather than automatically adding an ending.

There are spaces or punctuation at the edges

A leading or trailing space can stop a system from matching an address, even when the visible letters look correct. Punctuation may also have been copied accidentally, for example a comma or semicolon at the end. Remove it only if it is outside the address, not part of a separate field or a quoted CSV value.

One cell appears to contain several addresses

Some contact lists put multiple addresses in one cell, separated by commas or semicolons. Decide whether your destination system accepts that format. If it expects one address per cell, split the values into the right columns or rows without overwriting neighboring contact details.

The address looks normal but still may be wrong

An address can follow a familiar pattern and still have a misspelled name, a wrong domain, or a mailbox that no longer exists. A format check can flag obvious mistakes, but only the contact or a trusted source can confirm the correct address. Sending a test message is not a reliable way to check a large list, and delivery behavior varies between mail systems.

Correct the CSV without damaging other data

1. Check the whole row before editing. Confirm the name and any organization or phone number so you do not correct the wrong person's address. Similar names can appear more than once.
2. Fix only clear typos. Remove an accidental space or correct a character when the intended address is confirmed elsewhere. Do not guess a person's name, domain, or provider from context alone.
3. Keep CSV separators intact. A comma may separate columns, while a quoted value can contain a comma as ordinary text. Edit the email cell rather than copying a whole line into a new format, which can shift values into the wrong columns.
4. Do not remove rows just because an address is malformed. The contact may still have useful information. Mark the entry for follow-up or leave it unchanged until you can confirm it.
5. Review the saved copy. Reopen the exported file and check several corrected rows. Verify that names, email addresses, and neighboring fields still line up under the right headers.

Why a simple format check is not enough

Email systems allow some address formats that are uncommon in everyday contact lists, and different services apply different rules. A strict-looking pattern can reject an address that a particular mail system accepts. A relaxed check can let through a typo. Treat patterns such as one at sign and a domain ending as ways to find candidates for review, not as proof that an address is valid.

Also distinguish an address error from a delivery problem. A correctly written address may bounce because the mailbox was closed, the domain is not accepting mail, or the recipient's system rejected the message. Conversely, an address can look plausible without belonging to anyone. Confirm uncertain entries with the person or the system that supplied the contact list.

Your CSV stays on your device while you inspect and edit it in the browser. Keep a backup before making bulk changes, especially when the file contains your only copy of the contact list.