I want to create a "feature" for Gmail which keeps track of emails which did not get a reply. It shall check all sent emails for replies on a daily basis and list the ones which did not get a reply in a special folder/ add a tag so I can easily check them.
I have found a script out there already but it's not easy enough to add in a self serving way to unexperienced users' accounts (you have to download it and "install" it). Additionally it crashes frequently-it seems the amount of emails it may check is limited by Gmail.
I am not planning to develop it myself but am curious on you opinion of what's the best way to develop it (e.g. programming language) so I can look for the right type of developer.
Best, Mar
It is possible to do what you describe using Google Apps Script.
Essentially, you can write a script that activates on a time-based trigger, checks your inbox using GmailApp, and locates messages and adds new labels.
Note that you would have to ensure that you don't exceed the quota limitations; there are quotas for the number of possible Gmail actions taken and maximum script execution time. If you run into problems with these quotas, try breaking the problem into smaller pieces by processing smaller batches of mails with each execution.
Alternatively, you can write an application that manipulates your inbox using the Gmail API and one of the client libraries.