I would not play too much with alerts on this. It you import a file with 10000 records and 2000 countries are missing, you will receive 2000 alerts and probably seriously overload your mailbox doing this. Sure way tp make a good friend of your email admin
Rather use a smart list "person was created", source type is file import and subscribe to it.
You could also set up a smart campaign that listens for person was created via list import and country is empty.. and delete the lead as the flow step.
I know this is one of these frustrating things, but maybe look at source data quality - it is the old garbage in garbage out issue
The other thought might be to upload the data via a CRM that does allow you to enforce mandatory fields rules and have it pushed to Marketo via integration. We've adopted this approach successfully using Zoho and Marketo.
I would not play too much with alerts on this. It you import a file with 10000 records and 2000 countries are missing, you will receive 2000 alerts and probably seriously overload your mailbox doing this. Sure way tp make a good friend of your email admin
Rather use a smart list "person was created", source type is file import and subscribe to it.