PHP mail client, directly or through a database?

Question

PHP

Good afternoon, I am developing one service and there is a requirement to place an email client on it so that users can read and write letters from this service.
It turned out to read the headers and bodies of the letters, it even turned out to decode them normally, but there is one problem. All this takes a very long time (up to 10-15 seconds).
I use a set of regular PHP IMAP functions
I can assume that this time is spent on the imap_open () function.
And now the question itself is how normal mailers are made: directly with each request for a letter, they connect to the mail server, read data from there and close the connection, or read the data once and save it to the database and only occasionally check in the background whether New letter?
An example of how I read the body of the letter:

$mbox = imap_open("{" . $inputData['domain'] . ":143}INBOX", 
  $inputData['login'],
  $inputData['password']);
$body = imap_fetchbody($mbox,$msgno,1);	
$body = iconv("cp1251", "utf-8", $body);
imap_close($mbox);
return $body;

Answer 1

only occasionally in the background check if a new letter has arrived

yes, yes