What is the best practice for handling invalid email addresses in opt-in forms?

Marketer from Email Geeks advises putting some form of protection on your front door, or the ESP will be forced to take action, and your account will get deactivated until remediation has been completed.

Email marketer from Email on Acid suggests implementing typo checking in your forms to help users correct simple mistakes in their email addresses. This prevents invalid emails from being submitted due to typos.

Email marketer from Reddit user u/EmailPro responds that, after implementing front-end validation, the best practice is to monitor hard bounces and immediately remove those addresses from your list. Repeated sending to invalid addresses damages your sender reputation.

Email marketer from HubSpot Blog explains that, implementing regular list cleaning by removing inactive subscribers, unsubscribes, and bounced email addresses helps maintain a healthy sender reputation and improve email deliverability.

Email marketer from Stack Overflow User TechGuru shares using Javascript to validate the format of the email address. This provides immediate feedback to the user and reduces the amount of bad data sent to the server.

Email marketer from Neil Patel's Blog explains that using a double opt-in process is crucial. This involves sending a confirmation email to the address provided and only adding the address to your list once the user clicks the confirmation link. This helps ensure the email address is valid and that the user genuinely wants to subscribe.

Marketer from Email Geeks recommends at least captcha or confirmed opt-in (or both), noting that confirmed opt-in provides proof against spam accusations.

Email marketer from Sendinblue shares that implementing a CAPTCHA on opt-in forms can effectively prevent bots from submitting fake or invalid email addresses. This reduces the risk of adding these addresses to your mailing list.

Marketer from Email Geeks suggests Double Opt-in as a middle ground and recommends using all available layers including Captcha/bot scoring.

Marketer from Email Geeks explains that CAPTCHA is much improved and less of an obstacle for end users in 2023.

Marketer from Email Geeks advises always using a captcha, or two, to avoid complaints, mailbombing, and problems with invalid emails.

Email marketer from Mailchimp explains the importance of using email validation services to identify and remove invalid or risky email addresses before sending campaigns. This prevents bounces, improves sender reputation, and increases deliverability.

Email marketer from Email Marketing Forum User42 recommends using a third-party email validation service for real-time verification. These services can identify disposable email addresses, catch typos, and assess the risk level of an address.

Marketer from Email Geeks advises that hidden fields on the opt-in page and realtime email address validation are 2 other options besides or in addition to CAPTCHAs & COI. He also states COI doesn't solve subscription-bombing, it just converts it to confirmation-email bombing.

Marketer from Email Geeks identifies allowing bots to enter any data as a bad idea and recommends using captcha, suggesting reCAPTCHA as a frictionless option.

Expert from Spam Resource shares that you can start by validating the syntax of the email address. Email addresses have a specific format, and you should ensure that the entered address follows this format. You can use regular expressions or built-in functions in your programming language to validate the syntax. Check for invalid characters, missing parts, and proper domain name structure.

Expert from Word to the Wise emphasizes the importance of email address validation. She explains that it involves verifying the format and existence of an email address. This is achieved through syntax checks, DNS lookups, and SMTP pings. By validating email addresses, you can prevent bounces and improve deliverability.

Expert from Email Geeks describes the process of letting people give you anyone's email address without ensuring permission as "taking permission."

Expert from Email Geeks advises against accepting any email address and sending to it. He suggests client reputation services as an alternative to captchas for distinguishing between users and bots.

Expert from Email Geeks advises using a captcha even with Kickbox verification to prevent people from running large numbers of email addresses against your form.

Expert from Email Geeks recommends using Captcha because some addresses will deliver and you'll end up spamming. She also states that bot attacks harm real people and decrease your overall reputation and deliverability.

Expert from Email Geeks mentions using a behind-the-scenes assessment, like the sendex score from Kickbox, to silently drop low-quality signups.

Documentation from IETF explains the guidelines outlined in RFC 6530, RFC 6531, and RFC 6532 for supporting internationalized email addresses. Ensuring your system can handle these addresses correctly prevents valid users from being incorrectly rejected.

Documentation from OWASP shares guidance that from a security perspective, robust input validation, including email address validation, is essential to prevent injection attacks and other vulnerabilities. Rejecting invalid input early minimizes potential harm.

Documentation from RFC Editor outlines the importance of adhering to SMTP protocol specifications, which includes proper email address formatting. Invalid formats should be rejected at the submission stage where possible to avoid unnecessary processing.

Documentation from Microsoft Learn explains the use of regular expressions to validate email address syntax. This can be implemented on the client-side or server-side to filter out incorrectly formatted addresses before submission.