Emails with attachments from an alias are undeliverable to one of three aliases

T

Tom3900

New Member
OS Version(s)
  1. Windows
Outlook version
Outlook 2021 64 bit
Email Account
IMAP
Operating system::    Win 11
Outlook version:     classic Outlook
Email type or host:    IMAP
I have three outlook.com aliases, call them A1, A2, and A3.
If an email with an attachment is sent from either A1 or A2 to A3, that email is undeliverable.
But in all other cases, deliverability is not generally a problem, specifically:
#1. Emails without attachments from A1 and A2 to A3 are generally deliverable.
#2. Emails from any non-alias emails, with or without attachments, are generally deliverable to A1 and A2 and A3.
#3. All emails to A1 and A2 from any of the three aliases, with or without attachments, are generally deliverable.
Summary: The deliverability issue arises only with emails to A3, and having attachments, and sent from A1 or A2.
My Outlook.com account is accessed via emclient. Their support states that non-deliverability is determined by a Microsoft SMTP server, so not a client issue at all. The issue does not arise using outlook webmail, but emclient says webmail between two aliases would not go through a Microsoft SMTP server anyway, so the case of webmail is irrelevant here. Multiple file attachments and several attachment file types have been used for over two weeks, so no issues are arising from choices of attached files, which have been .pdf and docx. The problem is the same on Windows and Mac computers. Hopefully it is okay to post regarding emclient instead of classic Outlook client, since it has going away [had 2015 Office].
This problem is odd, but must have a solution in some way. The Microsoft support (bot) was not helpful.
 
These are all aliases on the same mailbox or are they 3 separate mailboxes?

If they are all address on the same mailbox, Microsoft is blocking them for security reasons - it's done it previously, but usually with all mail to and from the primary alias.

Is every attachment type affected - if you send a text file, does it go through? If that works, try either adding .txt to the filename or zip the files to send. There are some nasty exploits in pdf and docx files that they could be trying to block.

If separate mailboxes:
Do you get a bounce message back? If not, the gateway virus filter is blocking it.

And yes, asking for help with other clients is ok when the accounts involved are Microsoft Exchange. :)
 
Tom3900 said:
I have three outlook.com aliases, call them A1, A2, and A3.
If an email with an attachment is sent from either A1 or A2 to A3, that email is undeliverable.
But in all other cases, deliverability is not generally a problem, specifically:
#1. Emails without attachments from A1 and A2 to A3 are generally deliverable.
#2. Emails from any non-alias emails, with or without attachments, are generally deliverable to A1 and A2 and A3.
#3. All emails to A1 and A2 from any of the three aliases, with or without attachments, are generally deliverable.
Summary: The deliverability issue arises only with emails to A3, and having attachments, and sent from A1 or A2.
My Outlook.com account is accessed via emclient. Their support states that non-deliverability is determined by a Microsoft SMTP server, so not a client issue at all. The issue does not arise using outlook webmail, but emclient says webmail between two aliases would not go through a Microsoft SMTP server anyway, so the case of webmail is irrelevant here. Multiple file attachments and several attachment file types have been used for over two weeks, so no issues are arising from choices of attached files, which have been .pdf and docx. The problem is the same on Windows and Mac computers. Hopefully it is okay to post regarding emclient instead of classic Outlook client, since it has going away [had 2015 Office].
This problem is odd, but must have a solution in some way. The Microsoft support (bot) was not helpful.
Click to expand...
Thanks for responding. I have a new insight based on attachment size. But first your questions. I have one Ms outlook.com account, with three emails, all aliases, assuming "primary" designation is not meaningful. The new discovery is that the key element is attachment size, but why does one of three have a tight limit now?The situation summary is as follows:
Delivered emails examples:
A1 to A3, 12 kb attachment delivered
A1 to A2, 222 kb attachment delivered
A1 to A3, 222 kb attachment Undeliverable.
Inference: A3 has a very low limit for attachment size.
Background info: I have for a long time typically used A3 for file transfers from one home computer to another.
A theory of the case: A3 now has a very low limit for attachment size. The context is that I use emclient, and I block Onedrive and do not use it. Perhaps Ms servers are treating me as a Onedrive client with too many attachments sent of signficant size, so some algorithm blocks the size of A3 attachments. If this seems like the best theory to you, I supposed I chat more with Ms bots.
 
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