We have been encountering intermittent stability issues impacting the vmail1 mail service. Engineers are currently investigating/monitoring to alleviate the immediate issue and determine the root cause. During this time you may encounter issues accessing email via webmail or other devices such as laptops and smartphones.
UPDATE (2019-05-03 02:30):
Following investigation including support from the software vendor we have isolated what we believe to the trigger of the stability issues. Mitigations have been put in place to prevent the trigger from occurring whilst investigation are ongoing to establish a fix to prevent the stability issue in the trigger scenario.
UPDATE (2019-05-03 08:40):
At present the VMAIL1 mail service is functioning normally but until a software fix is provided we will be running enhanced monitoring/checks.