Description of problem:
When alerts module is configured with multiple email addresses, the emails are directed to only the 1st email ID added.

logs upon addition of email addresses via 
cmd : ceph config set mgr mgr/alerts/smtp_destination "pdhiran, ngangadh"

2023-08-01 10:30:05,346 [Dummy-1] [DEBUG] [root]  mgr option interval = 10.0
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_host = smtp.corp.redhat.com
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_destination = pdhiran, ngangadh
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_port = 25
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_ssl = False
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_user =
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_password =
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_sender = ceph-iad2-c01-lab.mgr
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option smtp_from_name = EC 8+6 Argo testing cluster
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option log_level = debug
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option log_to_file = True
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option log_to_cluster = False
2023-08-01 10:30:05,347 [Dummy-1] [DEBUG] [root]  mgr option log_to_cluster_level = info


logs upon sending email via : "ceph alerts send"
2023-08-01 10:30:53,974 [Dummy-1] [DEBUG] [root] _send_alert_smtp
2023-08-01 10:30:53,974 [Dummy-1] [DEBUG] [root] message: From: EC 8+6 Argo testing cluster <ceph-iad2-c01-lab.mgr>
Subject: HEALTH_OK
To: pdhiran, ngangadh
Message-Id: <169088585397.2.617791068636758749.redhat.com>
Date: Tue, 01 Aug 2023 10:30:53 -0000

HEALTH_OK


=== Full health status ===

2023-08-01 10:30:53,995 [Dummy-1] [DEBUG] [root] Sent email to pdhiran, ngangadh


Config :

# ceph config dump | grep alerts
mgr                                            advanced  mgr/alerts/interval                    10
mgr                                            advanced  mgr/alerts/log_level                   debug
mgr                                            advanced  mgr/alerts/log_to_file                 true
mgr                                            advanced  mgr/alerts/smtp_destination            pdhiran, ngangadh
mgr                                            advanced  mgr/alerts/smtp_from_name              EC 8+6 Argo testing cluster
mgr                                            advanced  mgr/alerts/smtp_host                   smtp.corp.redhat.com
mgr                                            advanced  mgr/alerts/smtp_port                   25
mgr                                            advanced  mgr/alerts/smtp_sender                 ceph-iad2-c01-lab.mgr
mgr                                            advanced  mgr/alerts/smtp_ssl                    false


Version-Release number of selected component (if applicable):
ceph version 17.2.6-70.el9cp (fe62dcdbb2c6e05782a3e2b67d025b84ff5047cc) quincy (stable)

How reproducible:
Always

Steps to Reproduce:
1. Install RHCS cluster
2. Configure email alerts, adding multiple email IDs.
3. run command : "ceph alerts send". The email is only sent to the 1st email.

Actual results:
Email not sent to multiple email IDs and only sent to 1st one in list

Expected results:
email alerts sent to all email IDs added.

Additional info: