Virgin Super Hub Blocks VPN Connections

By default Virgin Super Hub will block outgoing VPN traffic, even with firewall disabled. To allow all VPN connections perform following:

Export emails from Gmail for Work - downloading your data is disabled

Issue

A user is getting error when trying to export his emails via Google "Download you Data" feature. My Account > Personal Info and Privacy > Control your Content > Create Archive.

Downloading your data is disabled.
Downloading your data has been disabled for your account or organization by your domain administrator.

Draytek Vigor - You have reached the maximum number of permitted internet sessions...

Issue

Users accessing Internet via Draytek Vigor 2820 router occasionally get following message in their browsers and can not longer access Internet:

You have reached the maximum number of permitted Internet session.
Please close one or more application to allow further Internet access.
Contact your system administrator for further information.
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Emails to BT Internet recipients delayed (SMTP 421 Too many messages)

Issue

Users with IMAP mailboxes hosted on one.com are getting 421 bounces when sending emails to BT Internet customers:

This is the mail system at host mailrelay5.public.one.com.

####################################################################
# THIS IS A WARNING ONLY. YOU DO NOT NEED TO RESEND YOUR MESSAGE. #
####################################################################

I'm sorry to have to inform you that your message has not yet
been delivered to one or more recipients. It's attached below.

<This email address is being protected from spambots. You need JavaScript enabled to view it.> delayed: btinternet.com->MX:
421 Too many messages (1.5.7.1) from 91.198.169.199
Reporting-MTA: dns; mailrelay5.public.one.com
Received-from-MTA: smtp; [192.168.3.86] (81.133.42.155)
Original-Envelope-Id: 6a014cd9-a323-11e5-be90-b82a72d03b9b
Arrival-Date: Tue, 15 Dec 2015 12:16:26 +0000

Final-Recipient: rfc822; This email address is being protected from spambots. You need JavaScript enabled to view it.
Action: delayed
Status: 5.4.7 (Message could not be delivered in the allotted time frame)
Remote-MTA: dns; btinternet.com->MX
Diagnostic-Code: smtp; 421 Too many messages (1.5.7.1) from 91.198.169.199

Emails do get delivered eventually, but after few hours delay.