Ancestry, FTDNA, and MyHeritage have note fields for each of your DNA matches. This is a great way to record when you attempted contact, whether or not they answered you, their GEDmatch number if they have uploaded, MRCA if you have figured it out, etc.
If you want to make contact using Ancestry it will be via an internal message. The messages are held in a central location and not attached to the individual match so the notes field will help you keep things straight.
FTDNA does not have an internal messaging system and contact is done via email. Again, the notes field helps you keep track of attempts to contact.
23andMe does not have a notes field but does has a message box that holds all of the back and forth conversations that is attached to each individual match which is very useful. You don’t need a notes field.
GEDmatch does not have a notes field. It would be VERY useful here to know who you have contacted and who you still need to contact. Contact with matches is done via email. I will be suggesting this to them.