Google does not support this.
It is possible write a Google Apps Script, possibly/probably including the Gmail API , to generate an email that has the appearance of being an auto-reply (a "pseudo-autoreply"). There are many precedents for this. However these do not have the character of auto-reply emails, and they have some inherent limitations.
- auto-reply is triggered when an email is received. Apps Script has no equivalent; however depending on the "urgency" of generating the pseudo-autoreply, a time-driven trigger might be used to scan the inbox and execute the script.
- auto-reply does not mark the relevant message as "read". Depending on your needs, a pseudo-autoreply might need to avoid marking a message as read but in that case, it would need to label that message in such a way so that auto-replies are not continuously sent for that message. One option might be to use a single purpose-use label to denote that an autoreply has been sent.
- an auto-reply does not become part of any message thread. A pseudo-autoreply would need an appropriate title to avoid being added to a thread.
- genuine auto-replies have certain mail header values that identify their function, such as (but not limited to):
X-Autoreply
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