I have created a form that contains a button in which I am attempting to email to multiple addresses which are pulling from different fields upon clicking the button.  However, the button returns an error when clicked:

InfoPath cannot submit the form.
An error occurred while the form was being submitted.
The form cannot be submitted because some of the e-mail addresses cannot be resolved. If you know the values in the form that specify the e-mail addresses, revise them and try again.
The following addresses did not resolve in the To line: i:0#.w|nestle\ushelberma

Any ideas on why it is not submitting even though I see them resolve in the people picker?

The people picker does not display e-mail addresses. It displays user names. Domain\Username is not a valid e-mail address. This is why it won't resolve. For the e-mail submit to work, you need a valid e-mail address such as username@microsoft.com

I advise you to pick the multiple addresses from a list where you can create a People/Group column and add the names of recipients as list items or simply you may add email address as single line of text.

Or create a SharePoint group and add all email recipients to it and send email to this group email id on button click.

Are you sending the email via workflow or InfoPath code-behind?

Hello,

If you are trying to get email from person picker field then you won't be able to get email from accountid. You need to use userprofleservice.asmx web service to get email address of selected users.

http://thinketg.com/using-infopath-and-the-web-service-getuserprofilebyname/

http://sharepoint.stackexchange.com/questions/92171/codelessly-extract-emails-from-people-picker-in-infopath-2010

Hope it could help