imap-client | IMAP client as an AMD module | Runtime Evironment library

As @Max pointed out, you will need to decode the content using the encoding algorithm declared in the Content-Transfer-Encoding header.

In your case, it is the quoted-printable encoding.

You will need to decode the text of the message into an array of bytes and then you’ll need to convert that array of bytes into a string using the appropriate System.Text.Encoding. The name of the encoding to use will typically be specified in the Content-Type header as the charset parameter (in your case, koi8-r).

Since you already have the text as bytes in the buffer variable, simply perform the deciding on that:

I've had this before too. From the link in the error message you're receiving.

Allow less secure apps: If you don't use 2-Step Verification, you might need to allow less secure apps to access your account.

Here's a guide to do so

There is no standard way of obtaining the total size of a mailbox in IMAP. RFC 3501 does not include a command for that, and there is also no extension which provides such a functionality.

Your code could probably issue something like FETCH 1:* (RFC822.SIZE) and sum it up locally. That is quite a wasteful approach, unfortunately.

You should use EasyApache4 from the WHM interface. It will install php 5.5.x, php 5.6.x, php 7.x and even php 7.1.x. Then using MultiPHP from the same WHM interface you can customize the default php version on the server and also different php vesions for your cPanel users.

Do not manually install or delete php packages on the server or default php packages provided by cPanel. You risk to break stuff on the server which will lead to functionality issues.