Success and Failure Emails Sending when Smartbackup Fails

smartbackup was enabled on a newly promoted postgres master (dc1-mmprddb-22) and was failing to run successfully, due to an issue with the UUID in the conf file. However, after each unsuccessful smartbackup, an email was received reporting success as well as one reporting failure:

```
Message ID <5f4d2caf.1c69fb81.16269.0744SMTPIN_ADDED_MISSING@mx.google.com>
Created on: 31 August 2020 at 18:00 (Delivered after 1 second)
From: SmartBackup
To: unix@guardian.co.uk, andy.gallagher@guardian.co.uk
Subject: [UNIX TICKET] postgres backed up
The backup for database postgres on dc1-mmprddb-22 completed at Monday, 31-Aug-20 18:00:31 BST
```

```
Message ID <5f4d2cac.1c69fb81.3d45c.05ceSMTPIN_ADDED_MISSING@mx.google.com>
Created on: 31 August 2020 at 18:00 (Delivered after 2 seconds)
From: SmartBackup
To: unix@guardian.co.uk, andy.gallagher@guardian.co.uk
Subject: [UNIX TICKET] URGENT: postgres backup failed
The backup for database postgres on dc1-mmprddb-22 failed at Monday, 31-Aug-20 18:00:28 BST with the error Server error
```