generate an email in the same thread

[dpavlov]

I use a bot to generate an invoice and send it as a pdf attachment to customers. 

I want to be able to send a notification for overdue invoices in the same thread that i send the original invoice. 

I created the bot with the same subject, but it sends the email in a new thread. 

[Steve]

Threaded email is a function of the email client, not the email sender, as far as i know. Aside from giving the message the same subject, I know of no way to attach a message to an email thread.

[SkrOYC]

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@Steve wrote:

I know of no way to attach a message to an email thread

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Neither do I 

I tried to do it in the past but it seems there is some metadata that is shared between emails when you reply to one of them, so sadly it's not just the subject