Hello to all,
I need your help urgently, suddenly without changing anything, I can not send emails outside my domain from email logs I find this:

Jan 18 14:20:01 server1 dovecot: pop3-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:20:01 server1 dovecot: imap-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:20:01 server1 postfix/smtpd[2285]: connect from localhost[127.0.0.1]
Jan 18 14:20:01 server1 postfix/smtpd[2285]: lost connection after CONNECT from localhost[127.0.0.1]
Jan 18 14:20:01 server1 postfix/smtpd[2285]: disconnect from localhost[127.0.0.1]
Jan 18 14:25:01 server1 dovecot: pop3-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:25:01 server1 dovecot: imap-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:25:01 server1 postfix/smtpd[2356]: connect from localhost[127.0.0.1]
Jan 18 14:25:01 server1 postfix/smtpd[2356]: lost connection after CONNECT from localhost[127.0.0.1]
Jan 18 14:25:01 server1 postfix/smtpd[2356]: disconnect from localhost[127.0.0.1]
Jan 18 14:30:01 server1 dovecot: pop3-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:30:01 server1 dovecot: imap-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:30:01 server1 postfix/smtpd[2430]: connect from localhost[127.0.0.1]
Jan 18 14:30:01 server1 postfix/smtpd[2430]: lost connection after CONNECT from localhost[127.0.0.1]
Jan 18 14:30:01 server1 postfix/smtpd[2430]: disconnect from localhost[127.0.0.1]
Jan 18 14:32:10 server1 postfix/qmgr[9837]: BAF71C164: from=, size=1274, nrcpt=1 (queue active)
Jan 18 14:33:06 server1 postfix/smtp[2466]: BAF71C164: to=, relay=none, delay=58400, delays=58344/0.04/56/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)
Jan 18 14:35:02 server1 dovecot: pop3-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:35:02 server1 dovecot: imap-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:35:02 server1 postfix/smtpd[2508]: connect from localhost[127.0.0.1]
Jan 18 14:35:02 server1 postfix/smtpd[2508]: lost connection after CONNECT from localhost[127.0.0.1]
Jan 18 14:35:02 server1 postfix/smtpd[2508]: disconnect from localhost[127.0.0.1]
Jan 18 14:37:10 server1 postfix/qmgr[9837]: 319BCC166: from=, size=1650, nrcpt=1 (queue active)
Jan 18 14:37:10 server1 postfix/qmgr[9837]: 4F419C162: from=, size=1529, nrcpt=1 (queue active)
Jan 18 14:37:10 server1 postfix/qmgr[9837]: D9548C16C: from=<>, size=3858, nrcpt=1 (queue active)
Jan 18 14:38:06 server1 postfix/smtp[2542]: 319BCC166: to=, relay=none, delay=46615, delays=46559/0.06/56/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=pillsshop.info type=MX: Host not found, try again)
Jan 18 14:38:06 server1 postfix/smtp[2543]: 4F419C162: to=, relay=none, delay=46614, delays=46558/0.02/56/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)
Jan 18 14:38:06 server1 postfix/smtp[2544]: D9548C16C: to=, relay=none, delay=27953, delays=27897/0.03/56/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=risparmio-mail.com type=MX: Host not found, try again)
Jan 18 14:40:01 server1 dovecot: pop3-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:40:01 server1 dovecot: imap-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:40:01 server1 postfix/smtpd[2602]: connect from localhost[127.0.0.1]
Jan 18 14:40:01 server1 postfix/smtpd[2602]: lost connection after CONNECT from localhost[127.0.0.1]
Jan 18 14:40:01 server1 postfix/smtpd[2602]: disconnect from localhost[127.0.0.1]
Jan 18 14:42:10 server1 postfix/qmgr[9837]: A02CFC134: from=<>, size=3189, nrcpt=1 (queue active)
Jan 18 14:43:06 server1 postfix/smtp[2640]: A02CFC134: to=, relay=none, delay=4709, delays=4653/0.04/56/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)
Jan 18 14:45:02 server1 dovecot: pop3-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:45:02 server1 dovecot: imap-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:45:02 server1 postfix/smtpd[2683]: connect from localhost[127.0.0.1]
Jan 18 14:45:02 server1 postfix/smtpd[2683]: lost connection after CONNECT from localhost[127.0.0.1]
Jan 18 14:45:02 server1 postfix/smtpd[2683]: disconnect from localhost[127.0.0.1]
Jan 18 14:47:10 server1 postfix/qmgr[9837]: A983CC158: from=, size=824, nrcpt=1 (queue active)
Jan 18 14:48:06 server1 postfix/smtp[2771]: A983CC158: to=, relay=none, delay=42491, delays=42435/0.04/56/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)
Jan 18 14:50:02 server1 dovecot: pop3-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured
Jan 18 14:50:02 server1 dovecot: imap-login: Disconnected: rip=127.0.0.1, lip=127.0.0.1, secured

In my /etc/resolv.conf and /var/spool/postfix/etc/resolv.conf I have this:

domains members.linode.com
search members.linode.com
nameserver 109.74.192.20
nameserver 109.74.193.20
nameserver 109.74.194.20

Why can not I send email?
Please I need urgent help.
thanks

Are you running Plesk by any chance? If so, this may be a problem introduced with MU10 or MU11. Try updating from Plesk.

In the mean time try this from the command line:
restorecon /etc/resolv.conf
postqueue -f


MSJ

No, I'm using ISPConfig 3

Have you tried the 'restorecon /etc/resolv.conf' command?

What happens when you dig or ping a domain? Can either of those resolve the host?

With the command restoreconf says:
-bash: restorecon: command not found

With the ping command responds back to me the ip of my linode.
What else can I do?

Ping or dig another domain to see if you can resolve the domain. For example:
ping gmail.com
dig gmail.com mx

ping cnn.com
dig cnn.com mx

ping linode.com
dig linode.com mx

Running the command ping gmail.com
takes a long time and finally the result is:

ping: unknow host gmail.com

while running the command: dig gmail.com mx, the result is as follows:

connection timeout; no servers could br reached.

Same result for the other domains.

Why does this happen?

You're obviously not properly connecting to a nameserver or DNS servers.

What is in your hosts file?

Content file /etc/hosts

127.0.0.1 localhost
178.79.155.249   server1.queeninformatica.it   server1

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

domains members.linode.com
search members.linode.com
nameserver 109.74.192.20
nameserver 109.74.193.20
nameserver 109.74.194.20

I don't think domain is supposed to be plural. What happens if you change it to singular 'domain' instead of 'domains'? After you change it try to ping another domain again.

In fact, I changed from domains in domain in this way:

domain members.linode.com
search members.linode.com
nameserver 109.74.192.20
nameserver 109.74.193.20
nameserver 109.74.194.20

I restarted networking, then I launched:

dig gmail.com mx

but the result is the same:
connection timeout; no servers could br reached.

What linux distribution & version are you running?

Debian5
I know it's old, but I can not update because I have sites that run only on php 5.2.
So I'm afraid that updating the above sites would no longer work.
What I can say is that until a few days ago everything was working, suddenly the emails stopped working for no apparent reason.

I'm not here to judge your choice of linux Knowing helps when weeding through search results.

Did ISPConfig update recently? Have you tried their support forums?

Have you checked all the logs to see what type of error they have when you try to ping or dig?

Have you tried rebooting your server?

Thank you for your help, the answer to points:
I have not updated ispconfig and I have not even asked on their forum because I believe in truth that is not the problem.
I rebooted the server, but nothing changes.
I have not checked the error log ping or dig.
Where is it?
Thank you again.