I have a problem. Our workflow sends some notification to user with from address "no-reply.....@...com". But our users need possibility to reply someone who initiated this workflow sometimes. So the question is, how to change standard workflow no-reply email address to the address of person who initiated this workflow? I thought about custom action, but Office 365 sharepoint online has only declarative custom actions. Maybe I could use SMTP? If someone had some sort of problem, please help.
Sorry to break this news, but this is not possible. Emails are sent from defined outgoing email address and cannot be sent from initiators or custom users ID.
What you can do is, add related person in CC in those emails and you can put disclaimer in body asking to reply to the person in CC field, in case they have any issue.
The other answer here is incorrect.
You can send an email from any valid SharePoint user email address using the Call HTTP Web Service Action to send the email from the REST SendEmail endpoint.
[%Workflow Context:Current Site URL%]/_vti_bin/client.svc/sp.utilities.utility.SendEmail
When creating the Request Body dictionary variable, set the properties/From key value to the [%Workflow Context:Initiator%] variable with value type Email Address.