Thank you for taking care about the forwarding.
What I received was an email that announces the second part - but it contains no resume-link but a link to start a new questionnaire.
A resume-link looks like ...?i=ABDDFEG where the alphanumeric code is the interview token. This is simply the inteview's URL, and if using mailResume(), this one is sent.
The link in the email looks like ...?d=CDEFRG where the alphanumeric code is a one-time code to access the questionnaire. This is sent if you send the mailing manually or use mailSchedule().
Thererfore, I am quite sure that the email forwarded to me was not sent via mailResume().
If you can identify the case in your dataset, you can use the feature to change an existing interview case to create a new link for the respondent. Using the link from the original email (first invitation) may also work. You should find it in the address entry when you scroll down to the end.