Single Send Email API not respecting multiple addresses?


Hi! We’re trying to send transactional emails that have multiple Reply-To addresses, as denoted possible in the RFC 2822 spec. However, I’m unable to accomplish this. I’ve tried the following as values to the replyTo field in message, and none seem to work (the emails either fail to send or incorrectly parse the value):

['', '']
"<>, <>"
"Name <>,Name <>"
"Name <>, Name <>"

Some assistance in this matter would be appreciated. Thanks and have a great day!


Bump! Just curious if Hubspot internal has any details on the replyTo behavior. Thanks!


Bumping this again – this is a serious blocker for a business goal we have, and getting it resolved as soon as possible would be much appreciated or else we may have to look for solutions outside the HubSpot ecosystem.


@jmduke can you post the full call for me please. I’ll see if I can get you an answer


the replyTo is not a supported call in HubSpot. You can only have one replyTo email address in our single send API. My apologies for the inconvenience.


Hi @jmduke,

Just wanted to let you know that this is on my plate and we should hopefully have a solution to this issue out soon.

Note that this even fails with multiple Reply-To email addresses in an SMTP API call, which should be remedied as well.


Mike, this is great news – thanks so much! Please keep me posted and have a great Friday!


@jmduke This is al set. In the interest of backwards compatibility the new field is called “replyToList” and documented on



Hey Mike – just tried this out on our end and can confirm it works exactly as hoped! Thanks so much for your hard work.


Hey Mike (or anyone else!) We’re seeing a regression: we’re passing in multiple values via replyToList but only the first one is being parsed and sent in the final email. According to the API docs, nothing has changed:

Any idea what might be going on here? Thanks and have a great Thursday!


Tagging @Mike_Axiak to notify him


Hey @jmduke!

I have a suspicion about how this regression could have been introduced but I’ll need more information from you to be sure. I’ll DM you with more questions.


Sorry for the delay in response @pmanca and @Mike_Axiak: followed up with Mike via DM!


Thanks for closing the loop!


Just as a quick update — it’s been two weeks since I last heard from Mike. I poked him in DM as well but following up here as well to increase visibility!


Confirmed this morning that the issue’s been resolved! Thanks, all!