Hello shobhit03, are you sure about your SMTP server limitation? Did you try to compress your 4 attachments in an only one zip to see what happens?

Hi Smorele, Thanks for your prompt response!! Yes, i m sure about my SMTP server limitation.

Wow.....when i have zipped all 04 image files within single folder, attachment size reduced to 2.8MB from 3.4MB and my mail sent.. :)

Can you provide me the reason behind this, as my SMTP service provider is allegation for an issue with TB, however i am using updated 52.3.0 (32Bit) version

great, glad to see it helped. in general, there is no number of attachments limitation but it may be a clue. Can you try to send 4 or more (small pieces) to see if your limitation if here?

I have tested several mails with 04 or more attachments & observed that mail with attachment size >=03MB are not delivering and reflecting same error as above.

I did some research on the subject and it seems Thunderbird does not impose a restriction about attachment. Do you use a custom SMTP server or a famous (as Gmail for example) ? For more information and tips about sending a large attachment:

• How can I send a large attachment?

issues witin issues is what we see here perhaps.

1. Some SMTP server issue that error when your user name or password is incorrect OR you sending privilege has been stopped either due to service violations or things like exceeding the daily sending limit. That being additional to the per message limit.

2. Attachments, when mime encoded of inclusion in an email increase in size dramatically. in the order of a third (33%). The file size displayed is only marginally related to the size of the resulting email.

3. Your original image posting showed the error message stating the servers global message size limit is 4MB . 4194304byte is 4mb. So I have no idea where they plucked the 18mb from, but it would appear they forgot to tell their server that you are allowed to have messages that large.

I am using SMTP service from my employer...In order to confirm the same issue with an another mail client MS Outlook 2007, i found that mails up to 18MB attachment can be easily sent. So, it is confirm that issue is not with my SMTP service provider, it would be with TB..!!!

did you try to send the same attachment to the same recipient with MS Outlook 2007? Again, Thunderbird does not impose restriction on a number or size, but it me be a recipient's server restriction.

I did the same apart this i use 02 different mail-ids in same mail domain one at TB and another at MS Outlook 2007 every time mail successfully sent from MS outlook (upto 18 MB attachment size) but unable to do the same (restricted to 03 MB) for mail-id configured at TB...

shobhit03 said

(restricted to 03 MB) for mail-id configured at TB...

Well ask your mail provider (your emoloyer) why their mail server is reporting 4mb at the maximum limit if an email. You can continue to have a nice friendly discussion here forever, but it does not explain why the mail server is reporting t6he issue of 4mb being the limit.

My guess is outlook does not use SMTP, and the SMTP limit is 4mb and the server administrator, like many, has no idea about anything but Microsoft products.

I googled the issue and this is the answer Google supplied. https://support.microsoft.com/en-au/help/322679/how-to-set-size-limits-for-messages-in-exchange-server

As I do not use any Micoslop desktop or server software my ability to assist you is restricted to what is on the web. The limitations I linked to have been around now since at least the 2000 version of Exchange. Perhaps with the assistance of a link your server administrator will be able to correctly identify what the issue is.