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Maximum email size settings for Email Security.cloud

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Article ID: 150466

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Updated On:

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Email Security.cloud

Issue/Introduction

Email expansion is a common phenomenon in email processing.

When SMTP was designed back in the 1980's, it only had to transfer plain text. With the advent of HTML and Rich Text plus the need to add complex (all that's not text) attachments in the 90's, the system needed to change. This change meant that a decision had to be made to support these new files and keep all of the existing systems compatible. Designers opted to have all content converted to text using base64. The conversion of all these into base64 can cause the email size to expand during transmission.

The email size that the ClientNet portal uses is based on the final size of the email, post expansion, and the maximum value in bytes obtained by M * 1000 * 1024, M being the size in MB. To help you set up the email size that best suits your requirements we compiled the following table. To avoid rejection by email size, ensure the email you send is smaller than the recommended max size for the set portal size.

Resolution

Size relationship table

A configured email size X in ClientNet, means that it accepts emails up to size X from an email client.
This size is applied to the general email size option in ClientNet, as well as the various email size conditions in Data Protection.

Email size in ClientNet Threshold email size at email client
5.00 MB 3.50 MB
6.00 MB 4.20 MB
7.00 MB 4.90 MB
8.00 MB 5.60 MB
9.00 MB 6.30 MB
10.00 MB 7.10 MB
11.00 MB 7.80 MB
12.00 MB 8.50 MB
13.00 MB 9.20 MB
14.00 MB 9.90 MB
15.00 MB 10.70 MB
16.00 MB 11.40 MB
17.00 MB 12.10 MB
18.00 MB 12.80 MB
19.00 MB 13.50 MB
20.00 MB 14.30 MB
21.00 MB 15.00 MB
22.00 MB 15.70 MB
23.00 MB 16.40 MB
24.00 MB 17.10 MB
25.00 MB 17.90 MB
26.00 MB 18.60 MB
27.00 MB 19.30 MB
28.00 MB 20.00 MB
29.00 MB 20.80 MB
30.00 MB 21.50 MB
31.00 MB 22.20 MB
32.00 MB 22.90 MB
33.00 MB 23.60 MB
34.00 MB 24.40 MB
35.00 MB 25.10 MB
36.00 MB 25.80 MB
37.00 MB 26.50 MB
38.00 MB 27.20 MB
39.00 MB 28.00 MB
40.00 MB 28.70 MB
41.00 MB 29.40 MB
42.00 MB 30.10 MB
43.00 MB 30.80 MB
44.00 MB 31.60 MB
45.00 MB 32.30 MB
46.00 MB 33.00 MB
47.00 MB 33.70 MB
48.00 MB 34.40 MB
49.00 MB 35.20 MB
50.00 MB 35.90 MB
51.00 MB 36.60 MB
52.00 MB 37.30 MB
53.00 MB 38.00 MB
54.00 MB 38.80 MB
55.00 MB 39.50 MB
56.00 MB 40.20 MB
57.00 MB 40.90 MB
58.00 MB 41.70 MB
59.00 MB 42.40 MB
60.00 MB 43.10 MB
61.00 MB 43.80 MB
62.00 MB 44.50 MB
63.00 MB 45.30 MB
64.00 MB 46.00 MB
65.00 MB 46.70 MB
66.00 MB 47.40 MB
67.00 MB 48.10 MB
68.00 MB 48.90 MB
69.00 MB 49.60 MB
70.00 MB 50.30 MB
75.00 MB 53.90 MB
80.00 MB 57.50 MB
85.00 MB 61.10 MB
90.00 MB 64.70 MB
95.00 MB 68.30 MB
100.00 MB 71.90 MB
105.00 MB 75.50 MB
110.00 MB 79.10 MB
115.00 MB 82.70 MB
120.00 MB 86.30 MB

 

Additional Information

Note that different elements types have slightly different expansion ratios. The average email growth in bytes is roughly (n + 2 - ((n + 2) % 3)) / 3 * 4, where n is the original size in bytes, with the resulting values converging to 4/3 or 1.33(3). We have observed a variable growth between 1.33(~33%) and 1.35(~35%) depending on the files present in the emails and overall initial size of the email.

The preceding table is based on an expansion ratio between 1.33(3) and 1.35(5). The resulting values are the highest value which at 1.33(3) passes. There's a slight margin of up to 0.25Mb in some sizes. Try to stay under the referenced size value in the table in relation to the size that is set in the portal to ensure that the email isn't stopped incorrectly. The expansion is based on the type of files. This means that even if you have two emails that have an overall client-side size of 10Mb, and their components fairly are different, the final expanded email size are different. Hence the ratios.