Thanks for answer, duncanc! English is not my native language. I need some time for understanding technical details of documentation.
The three questions.
is it possible, after one time subscribing receive the series of pre-arranged letters? Each letter with a certain delay.
As I understood for this need to configure CRON?
Or sending series of letters with intervals is not impossible for one subscription?
@AlexT Yes it is possible to have a series of autoresponders, each sending a different campaign after a certain period from subscription. But it is not really practical to try to do that with short time periods because of the frequency of running process queue. In your example you would probably need to have the cron job run every few minutes.
Also, the period is from when the person subscribed, not confirmed the subscription, so you might be sending the autoresponder campaign before he has confirmed.
You need to use a cron job to run process queue so that the email sending is automated.