Is it possible to use a field other than email for the session?

Can I simply email a unique identifier to a respondent to complete the form?  Will the page breaks result in partial completion of the form to be saved?  I haven't seen an example of using a unique identifier that is not include the email address of the respondent.

Yes, it is possible to do it through a Unique ID.

1) First, setup you unique ID: https://www.jotform.com/help/79-How-to-Add-Custom-Unique-IDs-to-your-Form-Submissions 

2) Then create the URL session, in this case I have done it in the Thank You page:

Here is my session that I have opened with the ID number "1": https://form.jotform.com/70278614474966?session=1 

Let us know if you need more help.

By providing the URL session with ID to a respondent, can the respondent open the form from multiple computers and have jotform save the responses (by page with page breaks) before submitting?  

Does this enable a respondent to complete part of the form and then send it to another person to complete the rest of the form, by providing the second respondent with the same URL with ID?

Thanks.

1) Yes, the respondent can open the form from any other computer, the responses will be saved before submitting.

2) Yes, once the respondent fills his part(without submitting the form), he can share the URL with the session ID to someone else, and this new person can continue filling the form.

Let us know if you need more help.