Configure Postfix to Send Mail Using an External SMTP Server

Sometimes due to network configuration you cannot use your SMTP server and you want to send emails through a proxy/relay. Below you can find how to configure a linux machine so that to act as an SMTP relay and forward emails to one SMTP server.

First if not installed you should install postfix package for your linux server depending on the distribution. For example on a RedHat server you should do:

sudo yum install postfix

Then you should edit the below postfix configuration lines. Postfix configuration is handled by /etc/postfix/main.cf

  • Change inet_interfaces from localhsot to all
inet_interfaces = all

Configure the source from which the emails will be sent. For example you can use a specific host or a subnet of hosts. In my case I chose a subnet so the second line should be uncommented.

#mynetworks_style = class
mynetworks_style = subnet
#mynetworks_style = host
  • Configure your subnet source Address and mask.
You can also specify the absolute pathname of a pattern file instead
of listing the patterns here. Specify type:table for table-based lookups
(the value on the table right-hand side is not used).

mynetworks = 192.168.0.0/16, 127.0.0.0/8
#mynetworks = $config_directory/mynetworks
#mynetworks = hash:/etc/postfix/network_table
  • Add your SMTP server address in the latest line
#relayhost = $mydomain
#relayhost = [gateway.my.domain]
#relayhost = [mailserver.isp.tld]
#relayhost = uucphost
relayhost = [IP_Address]

Finally test your configuration by a powershell command to verify the functionality.

Send-MailMessage -From "sender@mail.com" -To "recipient@mail.com" -Subject "test email" -Body "test subject" -SMTPServer IP_Address

Veeam Backup fails with log message: CBT Data is Invalid

Having your backup jobs fail is really a frustrating experience. 99,5% of the time, i’m experiencing successful backups, either over TSM, or Veeam Backup.

However, there were more than a handful of times that the CBT (Change Block Tracking) stopped working, generally causing backup jobs to fail.

The message listed in the Action log is the following:

CBT data is invalid, failing over to legacy incremental backup. No action is required, next job run should start using CBT again.
If CBT data remains invalid follow KB1113 to perform CBT reset. Usual cause is power loss.

I’ve tried to narrow the reasons this happens, to mostly being Datastore capacity outage or the speed of snapshots being removed during the backup process.

Luckily, there is a solution and it lurks in the VMWare KB2139574 (Resetting Changed Block Tracking for VMware vSphere virtual machines) .

You can generally follow one of the two recommended actions according to VMWare:

  • Power off the VM and reset CBT
  • Run the provided script to┬áreset CBT on all VMs, which uses a snapshot method to save having to power the VMs off.

Personally, although i have tried both actions, i prefer the second approach, as most of the virtual Infrastructures contain VMs that are not easy to power off, or have different maintenance windows.

In any case, after reattempting to execute the Veeam backup job, the error is no longer there, and Change Block Tracking is back in use.