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This is done by your email client, not the sender. Here are Gmail's rules. Emails are grouped if each message meets the following: - The same recipients, send

• xyst 2y ago
  > The same recipients, senders, or subject as a previous message The recipient is the same (me@domain.com) The sender is the same (messenger@messaging.squareup.com) But subject differs depending on vendor. I could get emails from square with these subject lines: - “Receipt from {vendor1}” - “Receipt from {vendor2}” - “Receipt from {vendor3}” Which does lead me to suspect it’s a header as the Google docs indicate. But the headers in each message are different. I compared the messages to a group email convo I created between ‘me@domain.com’ and ‘me@gmail.com’ to compare and couldn’t find any similar header. There was a “in reply to” header but that same header was not found in square emails > Sent within one week of a previous message I have gone 1-2 weeks without interacting with a square enabled vendor in the past, so I don’t think this it.