[FIX] Allow e-mail channel to be used without default department. (#23945)

* [IMPROVE] Allow e-mail channel to be used without default department.

* [FIX] Trasferring to wrong department for incoming emails (#23950)

Co-authored-by: Murtaza Patrawala <34130764+murtaza98@users.noreply.github.com>

app/livechat/server/lib/Livechat.js

@@ -319,6 +319,8 @@ export const Livechat = {
 
 	setDepartmentForGuest({ token, department } = {}) {
 		check(token, String);
+		check(department, String);
+
 		Livechat.logger.debug(`Switching departments for user with token ${ token } (to ${ department })`);
 
 		const updateUser = {

server/email/IMAPInterceptor.ts

@@ -57,7 +57,7 @@ export class IMAPInterceptor extends EventEmitter {
 		});
 
 		this.imap.on('error', (err: Error) => {
-			this.log('Error occurred ...');
+			this.log('Error occurred: ', err);
 			throw err;
 		});
 	}

server/features/EmailInbox/EmailInbox_Incoming.ts

@@ -30,7 +30,7 @@ type FileAttachment = {
 const language = settings.get<string>('Language') || 'en';
 const t = (s: string): string => TAPi18n.__(s, { lng: language });
 
-function getGuestByEmail(email: string, name: string, department?: string): any {
+function getGuestByEmail(email: string, name: string, department = ''): any {
 	logger.debug(`Attempt to register a guest for ${ email } on department: ${ department }`);
 	const guest = LivechatVisitors.findOneGuestByEmailAddress(email);
 
@@ -43,6 +43,11 @@ function getGuestByEmail(email: string, name: string, department?: string): any
 				previousDepartment: guest.department,
 				newDepartment: department,
 			});
+			if (!department) {
+				LivechatVisitors.removeDepartmentById(guest._id);
+				delete guest.department;
+				return guest;
+			}
 			Livechat.setDepartmentForGuest({ token: guest.token, department });
 			return LivechatVisitors.findOneById(guest._id, {});
 		}
@@ -120,7 +125,7 @@ async function uploadAttachment(attachment: Attachment, rid: string, visitorToke
 	});
 }
 
-export async function onEmailReceived(email: ParsedMail, inbox: string, department?: string): Promise<void> {
+export async function onEmailReceived(email: ParsedMail, inbox: string, department = ''): Promise<void> {
 	logger.debug(`New email conversation received on inbox ${ inbox }. Will be assigned to department ${ department }`);
 	if (!email.from?.value?.[0]?.address) {
 		return;
@@ -134,6 +139,7 @@ export async function onEmailReceived(email: ParsedMail, inbox: string, departme
 	const guest = getGuestByEmail(email.from.value[0].address, email.from.value[0].name, department);
 
 	logger.debug(`Guest ${ guest._id } obtained. Attempting to find or create a room on department ${ department }`);
+
 	let room = LivechatRooms.findOneByVisitorTokenAndEmailThreadAndDepartment(guest.token, thread, department, {});
 
 	logger.debug({