Since the past few weeks, when I send messages to institutional Outlook accounts from DeltaChat, I get the following message:
This is the mail system at host mail.teapot.ovh.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system
<iso@sdu.dk>: host sdu-dk.i-v1.mx.microsoft[2a01:111:f403:ca09::6] said: 554
5.6.211 Invalid MIME Content: Single text value size (32822) exceeded
allowed maximum (32768) for the 'Chat-User-Avatar' header.
[AM8PR08MB6401.eurprd08.prod.outlook.com 2025-08-27T17:32:24.546Z
08DDE3A517C922EA] [AM8P189CA0017.EURP189.PROD.OUTLOOK.COM
2025-08-27T17:32:24.546Z 08DDE5471A41FDC8]
[AM3PEPF0000A797.eurprd04.prod.outlook.com 2025-08-27T17:32:24.551Z
08DDE24DCCE3A36A] (in reply to end of DATA command)
No matter how low the resolution of my DeltaChat avatar is, the reported size stays at 32822. I had to remove my avatar altogether to keep using DeltaChat. I believe this started happening before I upgraded to 2.0.