https://sourceforge.net/p/isync/mailman/isync-devel/thread/Y2jnr8hESp1PUW%2B6%40bulldog/#msg37731764
https://sourceforge.net/p/isync/bugs/68/
https://sourceforge.net/p/isync/isync/ci/b6c36624f04cd388873785c0631df3f2f9ac4bf0/

From b6c36624f04cd388873785c0631df3f2f9ac4bf0 Mon Sep 17 00:00:00 2001
From: Oswald Buddenhagen <ossi@users.sf.net>
Date: Mon, 6 Jun 2022 11:55:37 +0200
Subject: [PATCH] work around "unexpected EOF" error messages at end of SSL
 connections

gmail apparently doesn't send a close notification (SSL_shutdown())
before closing the TCP socket.
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -1620,6 +1620,7 @@ imap_socket_read( void *aux )
 					error( "IMAP error: unexpected BYE response: %s\n", cmd );
 					/* We just wait for the server to close the connection now. */
 					ctx->expectEOF = 1;
+					socket_expect_eof( &ctx->conn );
 				} else {
 					/* We still need to wait for the LOGOUT's tagged OK. */
 				}
@@ -1882,10 +1883,12 @@ static void
 imap_cleanup_p2( imap_store_t *ctx,
                  imap_cmd_t *cmd ATTR_UNUSED, int response )
 {
-	if (response == RESP_NO)
+	if (response == RESP_NO) {
 		imap_cancel_store( &ctx->gen );
-	else if (response == RESP_OK)
+	} else if (response == RESP_OK) {
 		ctx->expectEOF = 1;
+		socket_expect_eof( &ctx->conn );
+	}
 }
 
 /******************* imap_open_store *******************/
--- a/src/socket.c
+++ b/src/socket.c
@@ -810,6 +810,15 @@ socket_expect_activity( conn_t *conn, int expect )
 		conf_wakeup( &conn->fd_timeout, expect ? conn->conf->timeout : -1 );
 }
 
+void
+socket_expect_eof( conn_t *sock )
+{
+#ifdef SSL_OP_IGNORE_UNEXPECTED_EOF  // implies HAVE_LIBSSL
+	if (sock->ssl)
+		SSL_set_options( sock->ssl, SSL_OP_IGNORE_UNEXPECTED_EOF );
+#endif
+}
+
 int
 socket_read( conn_t *conn, char *buf, uint len )
 {
--- a/src/socket.h
+++ b/src/socket.h
@@ -142,6 +142,7 @@ void socket_start_tls(conn_t *conn, void (*cb)( int ok, void *aux ) );
 void socket_start_deflate( conn_t *conn );
 void socket_close( conn_t *sock );
 void socket_expect_activity( conn_t *sock, int expect );
+void socket_expect_eof( conn_t *sock );
 int socket_read( conn_t *sock, char *buf, uint len ); /* never waits */
 char *socket_read_line( conn_t *sock ); /* don't free return value; never waits */
 typedef enum { KeepOwn = 0, GiveOwn } ownership_t;