I have been unable to remain in contact with people who do not use email except for a handful of special people. I wonder with how many people average netizens keep in touch by email. As for as I am concerned, 200 people seem to be the maximum. On the one hand, new email addresses are being added to my email address book, but on the other hand, I am forced to clean it up by deleting those addresses of people who consistently ignore my sincere questions by email or with whom I have not exchanged any message for a long period of time (let's say at least a few years). Then the number of email addresses never exceeds 200.
Rather recently I read an online article to the effect that 250 seems to be the maximum number of people average email users can keep in touch with. So my number seems to match this number if I add the addresses of about 50 mailing lists and email newsletters I subscribe to. With these addresses included my email address book has never exceeded 250 email addresses, but I have no idea why this number is the maximum for me, too.
Email is not the only way of keeping in touch with others electronically. There are a plethora of social network services, including Facebook and Twitter. They seem to have grown in popularity so much that someone who does not have a Facebook account does not exist electronically for many netizens. Personally I have never felt any need to join such services for a number of reasons, including my impression that many postings there are quite narcissistic, though I do find one advantage of social network services to email, which is that they are far less binding.
In spite of the reservations I have about these services I have been using one social network service for quite some time, and it is for purely academic purposes - Academia.edu (my account is http://biu.academia.edu/tsvisadan/). In this service you can follow the academic activities, especially publications of your fellow researchers. I wish more researchers, especially those whose scholarly outputs interest me, joined this highly useful service, and more of those who have already joined it updated their respective pages, for example, by uploading their new publications. Unfortunately, I know quite a few researchers who are addicted to Facebook and/or Twitter but have not used this academic social network service.
Again its advantage is that it allows me to keep in touch electronically with those researchers with whom I would not be able to do so by email. But there seems to be a limit to the number of researchers you can follow in this means of electronic communication, too. Even if all the researchers on the planet joined it, I would not be able to follow more than 200, including those researchers whom I know personally and those who are towering figures in my research interests.