I don't know what the turn round time is for this function, I don't know if you would even get a reply. I'm not sure because, technically your submission doesn't have an email contact (e.g. I don't think they check your system).
There are many unknowns (certainly to me), is this from an email and I don't know if it is the whole email or an attachment.
You could try this, to check if it is no longer detected. Use the Extract option (give a temporary folder, not the original) on the file in the chest, when it is extracted there if it is detected again you know it is still considered malware, etc. When Avast alerts don't send it to the chest again and then try and submit that as a possible false positive.
Reporting Possible False Positive File or Website -
https://www.avast.com/false-positive-file-form.php. Normally you would get a response in a day or two.
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This is where it becomes very unclear for me, if it is found to be an FP and this is an email (it doesn't really have a file structure) or an email attachment I don't know how these are dealt with. For a bog standard file it can be placed back in the folder it came from and you should be good to go. But for an email file or attachment, many email programs don't hold emails individually but in the inbox, etc.
This is basically a big file (possibly compressed) and outside of that folder you can't just insert it back in there as it could corrupt the whole folder, which could result in the loss of the emails in that folder.
If an attachment it is in itself a file with an extension that can be opened, run outside of the email so doesn't really present as much of a problem, as for the most part you would have extracted that in order to view/run.