Here is a Python solution using regular expressions: ```python import re text = "Contact information:\n1. John Doe - john.doe@example.com\n2. Jane Smith - jane@smith-family.net\n3. support@company.co.uk\n4. info@subdomain.example.org\n5. Invalid email: not.an.email.com\n6. Another invalid: @missing-username.com" emails = re.findall(r'[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+', text) print(','.join(emails)) ``` This script uses the `re.findall()` function to find all substrings in the text that match the regular expression pattern for a valid email address. The pattern `[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+` matches any string that starts with one or more alphanumeric characters, followed by an '@' symbol, followed by one or more alphanumeric characters, a dot, and finally one or more alphanumeric characters. The `join()` function is then used to combine the list of email addresses into a single string, separated by commas.