How can I group email messages together using Message-ID or VERP?

Email marketer from Reddit suggests using a combination of `Message-ID`, `In-Reply-To`, and `References` headers to reconstruct email threads. However, notes that these headers can be manipulated or missing, so it's not a foolproof method.

Email marketer from Litmus explains Email clients use a combination of the subject line, and References/In-Reply-To headers. The References/In-Reply-To headers are the most accurate way to thread email messages.

Email marketer from Email Geeks notes some message IDs are recipient specific, so grouping at the campaign level may not work, supporting VERP as a better route.

Email marketer from Mailjet explains the importance of headers. Important Headers for threading email messages are Message-ID, In-Reply-To, and References.

Email marketer from Email Marketing Forum suggests that if you control the sending process, embedding a custom campaign identifier in the Message-ID or a custom header can help group messages. This approach is more reliable than relying solely on standard headers.

Email marketer from Super User explains that the 'References' and 'In-Reply-To' headers are designed for threading. 'In-Reply-To' points to the parent Message-ID, while 'References' contains a list of Message-IDs in the thread. However, not all email clients implement these correctly.

Email marketer from Mailgun shares that to reliably track and group emails, use custom headers for campaign identifiers. These are less likely to be altered and provide a consistent way to group emails, supplementing the standard Message-ID.

Email marketer from Stack Overflow shares that Message-IDs should be globally unique, but in practice, some systems might generate them in a predictable manner. You can use this to group messages, but it's not guaranteed to work reliably across all email providers.

Email marketer from Email Uplers explains to group emails into threads, you need to use the In-Reply-To and References headers. The In-Reply-To header specifies the Message-ID of the email you’re replying to, and the References header lists all previous Message-IDs in the conversation.

Email marketer from Sendgrid shares the best practice to use custom headers with your unique identifiers when grouping messages together to allow filtering and message grouping for campaigns.

Expert from Email Geeks mentions the data is probably in the VERP string, but it may be more or less opaque.

Expert from Word to the Wise explains that Message-ID should be unique for each email. For threading, the In-Reply-To and References headers are important. Not all systems correctly implement these, impacting threading reliability. Custom headers and campaign IDs can help for internal tracking.

Expert from Email Geeks explains MessageID is dictated by RFCs with the constraint of being globally unique and in the form of an email address, though many MTAs violate the email address constraint. MessageID doesn't always survive the SMTP process, as it can be removed and replaced. Also suggests to look at VERP strings as they are more likely to contain useful information.

Expert from Email Geeks recommends using VERP rather than the messageID if you’re using Salesforce. The data you want is in the VERP string. Message IDs are unique to the email, and many are just random strings. VERP strings are more likely to contain useful campaign/recipient/send information. Also suggests some ESPs use header fields for that information.

Documentation from LimiLabs explains VERP (Variable Envelope Return Path) which modifies the Return-Path address for each recipient. This allows senders to identify the exact recipient that caused a bounce, aiding in list management and grouping messages related to bounce events.

Documentation from RFC Editor explains that the Message-ID field contains a single unique message identifier. It is globally unique and immutable over the lifetime of the message. The format is addr-spec (e.g., <local-part@domain>).

Documentation from Oracle explains The Message-ID header is a unique identifier for an individual email message. The References header is used to link related messages together in a conversation thread.

Documentation from IETF explains that VERP is used to embed recipient-specific information in the return path, facilitating automated bounce processing. By analyzing the return path, you can identify which recipient caused a bounce and group related messages.

Documentation from Microsoft Learn explains that you can use the `In-Reply-To` and `References` header fields to correlate email messages in a thread. `In-Reply-To` contains the Message-ID of the message being replied to, while `References` contains a chain of Message-IDs from previous messages in the thread.