VT7.3 only sends a single maill even though multiple recipients are selected

VT7.3, when e-mail is composed and i have multiple VALID recipients in the TO field and hit 'send', mail is only sent to the ONE recipient. If i flip the recipients in the field, again, mail is only sent to the ONE_ recipient.

Is this a known bug/limitation?

mail.log only shows a single recipient in mail delivery. So vtiger is only generating a single mail.

Logs (vtigercrm.log):

Sat Dec 5 21:16:41 2020,656 [6878] DEBUG VT - Prepared sql query parameters : [77310,from_email,,[email protected]]
Sat Dec 5 21:16:41 2020,656 [6878] DEBUG VT - Prepared sql query parameters : [77310,saved_toid,,["[email protected]","[email protected]","[email protected]"]]
Sat Dec 5 21:16:41 2020,807 [6878] DEBUG VT - Prepared sql query parameters : [[email protected],27223]```

Log (mail.log)

```Dec 5 22:16:41 ucs postfix/smtpd[23795]: connect from unknown[192.168.0.3]
Dec 5 22:16:41 ucs postfix/smtpd[23795]: B6EB19EBC1: client=unknown[192.168.0.3]
Dec 5 22:16:41 ucs postfix/cleanup[23798]: B6EB19EBC1: [email protected]
Dec 5 22:16:41 ucs postfix/qmgr[2774]: B6EB19EBC1: [email protected], size=1089, nrcpt=1 (queue active)
Dec 5 22:16:41 ucs postfix/smtpd[23795]: disconnect from unknown[192.168.0.3] ehlo=2 starttls=1 mail=1 rcpt=1 data=1 quit=1 commands=7
Dec 5 22:16:42 ucs postfix/lmtp[23799]: B6EB19EBC1: [email protected], relay=127.0.0.1[127.0.0.1]:2003, delay=0.32, delays=0.08/0.01/0.05/0.18, dsn=2.1.5, status=sent (250 2.1.5 [email protected] Ok)```

Howto debug further?