Email technical specifications

Email specifications.

How PW Hosting email behaves, in numbers. For hostnames, ports, and how to set up a mail client, see mail settings.

This list is not exhaustive and is subject to change.

At a glance

50 MBLargest single
attachment
70 MBTotal message size,
everything included
100 recipientsPer message, counting
To, Cc, and Bcc

Review your current usage anytime at: Email → Sending & Delivery

How these are measured

Account-wideStorage and monthly
network traffic
Per messageSize, recipients,
and spam score
Per mailbox or domainFolders, aliases,
and connections

Storage and network traffic are shared across every mailbox, website, and file on the account.

Network limits apply to the entire account. Email is measured as total network traffic against one account-wide pool, shared with your websites and files, not counted per mailbox. Every address on the account draws from the same pool, which means heavy use by one mailbox reduces what is left for all the others. Accounts include 10 GB of monthly network traffic, and more can be added at $1 per GB per month.

Messages

These apply to each individual message. Size is measured on the finished message rather than the files you picked from your desktop, so headers, inline images, and encoding overhead all count toward the total. Every address in the To, Cc, and Bcc fields counts as one recipient, including addresses hidden in Bcc.

Limit Value
Largest single attachment 50 MBMeasured as the file on your disk
Total message size 70 MBMeasured after MIME encoding
Recipients per message 100To, Cc, and Bcc combined
Recipients per SMTP transaction 100Additional recipients are rejected
Spam score threshold 5.0A message scoring 5.0 or higher is treated as spam

The two size numbers differ because attachments are base64 encoded for transport, which inflates them by roughly a third. A 50 MB file arrives on the wire at about 68 MB, which is why the message ceiling sits at 70 MB rather than at 50. That gap is encoding overhead, not extra room for more files.

Your recipient's limit still applies. Most mail providers accept far less than we send — Gmail and Outlook both sit around 20 to 25 MB. A 50 MB attachment will leave PW Hosting successfully and then bounce at the far end. For anything much over 20 MB, send a download link instead of an attachment.

Spam scoring runs before a message reaches a mailbox. Anything below 5.0 is delivered normally. The score each message received, and the rules that contributed to it, are recorded in the message headers, so a message that was filtered unexpectedly can be checked against what actually triggered it.

Scores are cumulative. A message rarely reaches 5.0 on one factor alone. Missing or failing authentication records, spam-like phrasing and formatting, suspicious links, and a poor reputation for the sending domain each contribute a fraction, and it is usually several small factors together that push a message over the threshold. Keeping SPF, DKIM, and DMARC records correct for your domain is the single most effective way to keep your own outbound mail scoring low.

Forwarding and mailing lists have their own behavior rules beyond these counts. See the forwarding and mailing lists guide for how those work.

Blocked attachment types

Around 120 file extensions are rejected at the gateway regardless of size, because they are the formats most often used to deliver malware. Blocking happens in both directions, inbound and outbound. The categories below cover the list.

  • Executables and installers — .exe .com .bat .cmd .msi .msp .mst .scr .pif .lnk .jar .iso .chm
  • Scripts — .js .jse .vbs .vbe .vb .ps1 .psc1 .wsh .wsc .hta .sct .pl .ksh .csh .asp .bas
  • Web pages and shortcuts — .html .htm .shtml .shtm .url .website .asx
  • Macro-enabled Office documents — .docm .xlsm .pptm
  • Access and database files — .mdb .mde .adp .ade, and the rest of the Access .ma* and .md* family
  • Windows system and configuration files — .reg .cpl .sys .inf .ins .isp .vxd .scf .shs .hlp .gadget .theme
  • Self-extracting and legacy archives — .cab .ace .arj .sfx

Ordinary archives are opened and scanned, not blocked. .zip, .rar, .7x, .xz, .bz2, .lz, .alz, and .egg are accepted, but their contents are checked against the same list — a blocked file type inside an archive is still blocked. Everyday documents pass normally, including .pdf, .docx, .xlsx, .pptx, and .txt.

Storage and network traffic

Storage and network traffic are account-wide rather than per mailbox, and they are the same on every website plan. Your account gets one shared pool of each, used by your mailboxes, your websites, and your files together.

Limit Value
Included disk storage 10 GBShared across the whole account
Included monthly network traffic 10 GBShared across the whole account
Additional capacity $1 / GB per monthStorage or network traffic, added by the gigabyte

Neither pool is a fixed ceiling. If your account needs more of either, add capacity by the gigabyte at $1 per GB per month rather than changing your website plan — the plans differ on websites, databases, and performance, not on storage or traffic.

Going over the included pools may be billed as overage. Exceeding 10 GB of storage or 10 GB of monthly network traffic is generally handled as an additional charge at $1 per GB per month rather than by cutting off your mail. Open the Admin Portal to see how much of each pool is in use and which mailboxes are using it, so a larger invoice is not the first you hear about it. Emptying Trash and Junk across your mailboxes is usually the fastest way to bring storage back down.

Retention and encryption

Mail is encrypted where it is stored, and a few folders are cleared automatically so they do not grow against your storage pool forever.

Specification Value
Encryption at rest EnabledStored mail is encrypted on disk
Trash auto-purge 30 daysMessages in Trash are removed automatically

Nothing outside Trash is deleted on your behalf. Emptying Trash and Junk yourself is still the fastest way to recover space rather than waiting out the 30 days.

Mailboxes and aliases

Hosted email is billed per primary mail domain. Email aliases on that domain are included at no extra charge, and alias domains inherit the settings of the primary domain they belong to.

Folders and mailbox structure

Folder limits are enforced by the mail server itself, so they apply per mailbox and are identical on every plan and in every mail client.

Limit Value
Folders per mailbox 1,000Including Inbox, Sent, Drafts, Junk, and Trash
Maximum nesting depth 10 levels
Maximum folder name length 255 characters

Nesting depth counts every level from the top down, so Clients/2026/Q1/Invoices sits four levels deep and has six to spare.

Connections and authentication

Mail clients hold connections open, and a single account checked from a phone, a laptop, and a desktop at once can use more than you would expect. These caps keep one busy account from crowding out others.

Limit Value
Concurrent IMAP connections per mailbox 16
IMAP authenticated session timeout 30 minutes
IMAP idle timeout 30 minutes
IMAP unauthenticated timeout 60 seconds
Messages per SMTP session 333
Failed authentication attempts per session 3Each failure adds a 5 second delay before the session is closed

Repeated authentication failures are almost always a mail client still holding an old password after a password change. Update the saved password on every device, including phones.

JMAP

JMAP is the protocol behind webmail and the newer mail clients that support it. It has its own limits, separate from the IMAP and SMTP figures above.

Limit Value
Maximum upload size 50 MBPer uploaded file
Upload quota 50 MB
Unreferenced upload retention 1 hourUploads not attached to a message expire
Maximum request size 10 MB
Concurrent requests 4
Concurrent uploads 4
Method calls per request 16
Push subscriptions 15

Enforcement behavior

Size limits are permanent rejections. An oversized message will not be retried, and you will receive a bounce notice explaining which limit it exceeded. Send it again with a smaller attachment, or with a download link in its place.

Connection limits are temporary. When too many sessions are open at once, further connections are refused with a temporary 4xx response and your mail client retries on its own, usually without showing you anything at all.

Folder limits clear as soon as the underlying condition does: remove folders you no longer need, or flatten a tree that has grown too deep.

Storage and network traffic work differently from the rest. Rather than blocking mail, exceeding either pool is generally billed as overage at $1 per GB per month. Both pools are drawn down by every address on the account together, so the fix is rarely something a single mailbox can handle on its own. Check where the account stands in the Admin Portal rather than waiting for the invoice to tell you.

Hard bounces and spam complaints are handled separately from everything on this page and are documented in the hard bounces and spam complaints guide.