Is quoted printable text allowed in the List-Unsubscribe header?

Email marketer from Litmus Blog emphasizes the importance of testing email header compatibility across various email clients. He adds, that if you must use quoted-printable encoding, double-check how different clients render it.

Email marketer from Mailchimp specifies that while encoding the entirety of the List-Unsubscribe is not generally recommended, the associated URL should always be URL-encoded.

Email marketer from Email Geeks explains that if the ESP or mail stream is encoding headers, Hotmail might not decode it properly, displaying it as is. This can lead to issues where unsubscribe links don't appear correctly in some mail apps, causing complaints from senders.

Email marketer from SendGrid explains that if your List-Unsubscribe header includes a URL, ensure that the URL itself is properly URL-encoded (percent-encoded) to handle special characters. This is different from quoted-printable encoding of the entire header.

Email marketer from Email Geeks shares that the issue of quoted printable text in the List-Unsubscribe header not working is observed frequently in Hotmail mailboxes, while it seems to function correctly elsewhere.

Email marketer from Campaign Monitor emphasizes that keeping email headers as simple as possible can improve deliverability. Avoid complex encoding unless there is a clear need. In most cases a plain ASCII URL will work fine.

Email marketer from Mailjet Support explains that if you decide to use quoted-printable encoding in email headers like List-Unsubscribe, make sure to test thoroughly with different email clients and ISPs to ensure it is correctly interpreted. Poorly encoded headers can cause deliverability issues.

Email marketer from Email on Acid Blog advises that while technically you *can* encode parts of the List-Unsubscribe header, it's generally better to avoid it because of potential compatibility issues. Stick to URL-encoded ASCII characters if possible.

Email marketer from Reddit advises to keep List-Unsubscribe simple. If you use a URL, make sure it's properly encoded for the web (percent-encoding), but avoid quoted-printable unless absolutely necessary. Some ISPs and email clients might not handle it correctly, leading to broken unsubscribe links.

Email marketer from StackOverflow explains that generally it's safer to avoid encoding the List-Unsubscribe header if possible, and to use plain ASCII characters for maximum compatibility. If encoding is necessary, it's crucial to test thoroughly across different email clients.

Email marketer from SparkPost emphasizes compliance with email standards for headers. He adds, that avoid using non-standard encoding in headers as it increases the chances of deliverability problems.

Expert from Word to the Wise advises against using quoted-printable in the List-Unsubscribe header. While technically possible, it can create compatibility issues across different email clients, and best practice is to maintain ASCII compatibility.

Expert from Email Geeks explains that quoted printable text is likely not allowed in the List-Unsubscribe header in any useful way, based on RFC 2047 and 2369. He clarifies that RFC 2047 encoded words are only allowed in specific header fields like Subject, Comments, or within a 'phrase' before an email address in the From header. Using it elsewhere results in a badly formed header that may only work accidentally at some ISPs.

Expert from Word to the Wise explains that the usage of quoted-printable in the List-Unsubscribe header is problematic. While technically feasible, many ISPs and email clients may not correctly interpret the encoded characters, leading to unsubscribe failures. It's better to avoid it.

Documentation from ietf.org explains that RFC 2047 defines how to represent non-ASCII characters in email headers. It specifies that encoded words (using quoted-printable or base64 encoding) are only permitted in specific header fields like Subject, Comments, or certain address fields. The List-Unsubscribe header is not among those explicitly mentioned.

Documentation from Microsoft highlights that valid and properly formatted email headers are critical for email deliverability. Improper encoding in headers can cause filtering or rejection. Though it doesn't specifically discuss List-Unsubscribe, this principle applies broadly.

Documentation from Mozilla explains that header fields follow specific formatting rules, and while encoding is possible for certain characters, it needs to be done according to standards to ensure proper interpretation by mail clients. It doesn't explicitly address List-Unsubscribe, but the general guidance applies.

Documentation from ietf.org explains that RFC 2369 defines the format and usage of the List-Unsubscribe header. The RFC does not explicitly prohibit the use of encoded words within the URI or mailto: address. However, implementations must be cautious about compatibility issues and ensure that the resulting header remains valid and parsable.

Documentation from Apache explains that while MIME encoding (including quoted-printable) is supported for email content, its use in headers should be approached with caution. The best practice is to adhere to established standards and test for compatibility across different email clients.