Hotmail account has stopped receiving emails

My hotmail account has suddenly stopped receiving emails. I have checked the email rules (there are none), the blocked senders list (only has people I added on purpose), the safe senders list (a good chunk of the people emailing me are on it) and email forwarding (I don't have forwarding set up).

A few emails seem to make it through but the rest don't and the sender receives an email that says their email was undeliverable. I have emailed my hotmail address off my work account and experienced the same thing.

Frustratingly, support only seems to be able to contact me through email and only one of their emails so far have gotten through.

The undeliverable email received by the senders is as follows:

Diagnostic information for administrators:

Generating server: VE1EUR03HT101.mail.protection.outlook.com

[my email address]
Remote Server returned '< #5.4.300 smtp;550 5.4.300 Message expired -> 432 4.3.2 STOREDRV.Deliver; mailbox database thread limit exceeded[retryinterval=00:04:53.3288686][retryqueue=False][retryscopetype=DatabaseTenant]>'

Original message headers:

Received: from DB5EUR03HT098.eop-EUR03.prod.protection.outlook.com

 (10.152.20.203) by VE1EUR03HT101.eop-EUR03.prod.protection.outlook.com

 (10.152.19.149) with Microsoft SMTP Server (version=TLS1_2,

 cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P256) id 15.20.952.17; Wed, 18

 Jul 2018 19:30:21 +0000

Received: from DB5EUR03FT051.eop-EUR03.prod.protection.outlook.com

 (10.152.20.53) by DB5EUR03HT098.eop-EUR03.prod.protection.outlook.com

 (10.152.20.203) with Microsoft SMTP Server (version=TLS1_2,

 cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id 15.20.952.17; Tue, 17

 Jul 2018 06:50:03 +0000

Authentication-Results: spf=none (sender IP is 5.150.104.10)

 smtp.mailfrom=[domain of sender]; hotmail.co.uk; dkim=none (message not

 signed) header.d=none;hotmail.co.uk; dmarc=none action=none

 header.from=[domain of sender];

Received-SPF: None (protection.outlook.com: [domain of sender] does not

 designate permitted sender hosts)

Received: from out.mailprotect.org.uk (5.150.104.10) by

 DB5EUR03FT051.mail.protection.outlook.com (10.152.21.19) with Microsoft SMTP

 Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id

 15.20.952.17 via Frontend Transport; Tue, 17 Jul 2018 06:50:03 +0000

X-IncomingTopHeaderMarker: OriginalChecksum:05F92C82B4590055FC5464A7255A932F4BF5C396312FA770974A42215A37312E;UpperCasedChecksum:DFA8C1B0C59761CDA71CDE0CFE515F64CE8B878C98EC6D2A5D15DA8714523908;SizeAsReceived:1687;Count:23

Received: from [sender]

        by Atomwide MailProtect with SMTP

        id fJoBfUTSNgUD5fJoBfcOGk; Tue, 17 Jul 2018 07:50:03 +0100

X-MP-OriginatingIP: Q24QDvIOi2pBqjmkiWY2Ig==

X-MP-Out-ID: fJoBfUTSNgUD5fJoBfcOGk

Received: from [sender] by

 [sender] with Microsoft SMTP Server (TLS) id

 15.0.1156.6; Tue, 17 Jul 2018 07:49:20 +0100

Received: from [sender] by

[sender]
 with mapi id

 []; Tue, 17 Jul 2018 07:49:20 +0100

From: work email

To: broken hotmail

Subject: RE: Test

Thread-Topic: Test

Thread-Index: AQHUHZpatXrY4t/gF0WIqA1T7xV9C6SS+Ujg

Date: Tue, 17 Jul 2018 06:49:20 +0000

Message-ID: 

References: <*** Email address is removed for privacy ***>

In-Reply-To: <*** Email address is removed for privacy ***>

Accept-Language: en-GB, en-US

Content-Language: en-US

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Content-Type: multipart/alternative;

        boundary="_000_c1ffe7f70caf43b086b5da3bba1f4ef7A
[sender]
_"

MIME-Version: 1.0

X-CMAE-Envelope: MS4wfKmwJIG9uwtNn8CHssOquTZxkKNH/k4G3ACiOS339/bmp2eoWSqhEeQxvTNUUS3Sp/3sdo7KKJskKMNiGhQQJ19T7LwL7D6rlXSZrALYB/Uz0wsD37Vg

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