Postfix中commands=5导致自有域名邮件发送失败的问题求助

大家好，我目前遇到一个Postfix的奇怪问题，想请教一下各位大佬：我用Postfix发送邮件时，发给外部域名的邮件基本正常，但发送到自有域名（nvoids.com）的时候，偶尔会出现commands=5的情况，导致邮件发送失败，而且我完全找不到这些失败邮件的去向；但有时候Postfix又会显示commands=6，这时候邮件就能正常发送。

错误场景相关日志片段 #

disconnect from localhost[127.0.0.1] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
20FB641206: from=admin@nvoids.com, size=3149, nrcpt=1 (queue active)

完整错误场景Postfix日志 #

Aug 10 07:29:49 ubuntu postfix/smtpd[1669634]: connect from localhost[127.0.0.1]
Aug 10 07:29:49 ubuntu postfix/smtpd[1669634]: 20FB641206: client=localhost[127.0.0.1]
Aug 10 07:29:49 ubuntu postfix/cleanup[1669637]: 20FB641206: message-id=<632614904.2235.1691652589133@ubuntu>
Aug 10 07:29:49 ubuntu postfix/smtpd[1669634]: disconnect from localhost[127.0.0.1] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
Aug 10 07:29:49 ubuntu postfix/qmgr[533470]: 20FB641206: from=<admin@nvoids.com>, size=3149, nrcpt=1 (queue active)
Aug 10 07:29:49 ubuntu postfix/smtp[1669638]: 20FB641206: to=<emailid@gmail.com>, relay=gmail-smtp-in.l.google.com[142.251.167.27]:25, delay=0.54, delays=0/0/0.23/0.31, dsn=2.0.0, status=sent (250 2.0.0 OK  1691652589 d7-20020a0cb2c7000000b0063d456fcd44si447714qvf.515 - gsmtp)
Aug 10 07:29:49 ubuntu postfix/qmgr[533470]: 20FB641206: removed

正常发送场景（commands=6）的Postfix日志 #

Aug 10 07:29:44 ubuntu postfix/smtpd[1669634]: connect from localhost[127.0.0.1]
Aug 10 07:29:44 ubuntu postfix/smtpd[1669634]: 1B16341206: client=localhost[127.0.0.1]
Aug 10 07:29:44 ubuntu postfix/cleanup[1669637]: 1B16341206: message-id=<835472293.2234.1691652584108@ubuntu>
Aug 10 07:29:44 ubuntu postfix/smtpd[1669634]: disconnect from localhost[127.0.0.1] ehlo=1 mail=1 rcpt=2 data=1 quit=1 commands=6
Aug 10 07:29:44 ubuntu postfix/qmgr[533470]: 1B16341206: from=<admin@nvoids.com>, size=1043, nrcpt=2 (queue active)
Aug 10 07:29:44 ubuntu postfix/smtp[1669638]: 1B16341206: to=<emailid@gmail.com>, relay=gmail-smtp-in.l.google.com[142.251.167.27]:25, delay=0.6, delays=0.01/0/0.23/0.36, dsn=2.0.0, status=sent (250 2.0.0 OK  1691652584 o5-20020a05620a0d4500b00767507d715asi489272qkl.541 - gsmtp)
Aug 10 07:29:46 ubuntu postfix/smtp[1669639]: 1B16341206: to=<admin@nvoids.com>, relay=route1.mx.cloudflare.net[2606:4700:f5::c]:25, delay=2.6, delays=0.01/0/0.19/2.4, dsn=2.0.0, status=sent (250 2.0.0 Ok)
Aug 10 07:29:46 ubuntu postfix/qmgr[533470]: 1B16341206: removed

我的/etc/postfix/main.cf配置 #

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level=may

smtp_tls_CApath=/etc/ssl/certs
smtp_tls_security_level=may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination

myhostname = ubuntu
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = $myhostname, smtp.domain.com, ubuntu, localhost.localdomain, localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
inet_protocols = all

后来我自己注意到一个细节：当我只发送邮件给外部邮箱时，日志里会显示commands=5；但如果同时抄送给自有域名的admin@nvoids.com，就会显示commands=6，这时候邮件也能正常发送到两个收件人。

希望各位能帮我分析下问题出在哪，以及那些失败的邮件到底去哪了，谢谢大家！

备注：内容来源于stack exchange，提问作者Pradyut Bhattacharya