php function to validate an email address

Verifying email addresses is a common task in PHP, mainly by using the filter_var() function with the FILTER_VALIDATE_EMAIL filter. This is the easiest and reliable method. It can check the correctness of the email format, including the correct location of the @ symbol and domain name part, the valid characters of the local part, and the validity of the domain name format, but does not verify whether the mailbox is real; secondly, although it can be used for verification, due to the email grid The formula is complex, and custom regularity is prone to errors. It is not recommended unless there are special needs. In addition, you can optionally check whether the domain name has MX records in combination with the checkdnsrr() function to confirm that the domain name can theoretically receive emails, but this step may slow or fail due to DNS problems. Finally, the input should be cleaned before verification, such as using the FILTER_SANITIZE_EMAIL filter to remove excess characters to avoid verification errors; in summary, the recommended practices are: 1. Use filter_var for format verification; 2. Optionally add DNS checks; 3. Avoid custom rules; 4. Clean input before verification.

Validating an email address in PHP is a common task, especially when handling user registration, contact forms, or any kind of input where email format matters. While there's no one-size-fits-all solution due to the complexity of email standards, there are solid methods you can use to make sure an email is at least in a valid format.

Use filter_var with FILTER_VALIDATE_EMAIL

The simplest and most reliable built-in method in PHP is using filter_var() with the FILTER_VALIDATE_EMAIL filter. It's designed specifically for this purpose and handles most standard email formats correctly.

 $email = "test@example.com";
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
    echo "Email is valid.";
} else {
    echo "Email is not valid.";
}

This approach checks for:

• Proper placement of @ and domain part
• Valid characters in the local part (before the @)
• A valid domain name format

It won't check if the email actually exists—that requires additional steps like SMTP checks or sending a confirmation link.

Don't try to write your own regex unless you have to

Some developers try to write their own regular expressions to validate emails. While it's possible, it's also error-prone because the official email format is extremely complex.

A commonly used regex like this one:

 $email = "user.name@domain.co.uk";
if (preg_match("/^[a-zA-Z0-9._% -] @[a-zA-Z0-9.-] \.[a-zA-Z]{2,}$/", $email)) {
    echo "Valid format.";
}

...might work for most common cases, but still might miss some edge cases or block valid addresses. So unless you have a specific reason to use regex (like enforcing stricter rules for your app), stick with filter_var() .

Combine with DNS checks (optional but stronger validation)

If you want to go a step beyond format validation and check if the domain could receive emails, you can use checkdnsrr() to verify that the domain has valid MX records.

 $domain = substr(strrchr($email, "@"), 1);
if (checkdnsrr($domain, "MX")) {
    echo "Domain can receive email.";
}

Keep in mind:

• This doesn't confirm the email exists
• It only checks if the domain is configured to receive emails
• It can be slow or fail due to DNS issues

So it's a nice optional step but shouldn't be required unless you have a specific need.

Sanitize before validating

Before validating, it's a good idea to clean the email string a bit to avoid false negatives:

 $email = trim(filter_input(INPUT_POST, 'email', FILTER_SANITIZE_EMAIL));

Sanitizing removes unwanted characters like extra spaces or special symbols that might break the validation even if the user intended a valid email.

So to put it all together:

• Use filter_var($email, FILTER_VALIDATE_EMAIL) for most cases
• Optionally add DNS checks if you want stronger domain validation
• Avoid writing your own regex unless you have a clear reason
• Always sanitize the input before validating

Basically that's it.

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