Correspondence courses are the oldest form of distance education. It is so old that it predates the internet itself. The main difference between people who do correspondence courses and people who do their education through brick and mortar schools and colleges is that in the former, there is no direct interaction between instructors and students. Before the age of the internet, this interaction was via post and with the advent of the internet, it became online. In fact, correspondence course students interact even less with their instructors than learners who take standard online classes. This can be to the point where they might only hear from their professors when the latter is giving feedback on assignments that the students have completed.
However, even if that is the case, students can reach out to them over mail with the questions and concerns they have as they work through the course.
An advantage that correspondence courses offer is significant pace flexibility. Students are able to set their own pace to study the course. They can complete the work related to the course with little to no instructor intervention. They may register at any time, irrespective of semester timelines, under the condition that they complete the requirements of the course within a certain timeframe. Usually, students receive the materials required for the course at the time of enrollment and submit their work as they progress.
Some instructors offer continuous feedback and accept assignments on a regular basis, while some other instructors prefer students submit all their required work at one time. The student needs to be discussed with the instructor and come up with a plan accordingly.
However, it must be noted that correspondence courses are not for everyone. The student needs to know his or her strengths and weaknesses before making a decision.