Sigmera for Email Marketers
Email marketing runs on lists nobody kept tidy. A webinar signup sheet merged with a Shopify export merged with a form fill, and the ESP wants one clean row per person. Sigmera fixes that file in a browser tab — dedupe the email column, strip whitespace and stray capitals, split names for merge tags, normalise phone numbers for SMS consent — and the subscriber list never leaves your device.
The data problems you hit
- The same subscriber sits in the file three times because three sources spelled the address differently — [email protected], [email protected], and ' [email protected] ' with a leading space. Klaviyo skips repeated email addresses in the same file and recommends removing duplicates before you import to speed up processing, so those rows are wasted either way.
- Duplicate and dead contacts cost money. Mailchimp counts subscribed, unsubscribed, and non-subscribed contacts toward your monthly contact limit, and if your total goes past that limit at any point in the billing cycle you get an additional charge on the bill. A list padded with repeats is a list you are paying twice for.
- Malformed addresses bounce. Mailchimp asks you to review the email column for syntax errors, unsupported characters, and extra spaces before importing, and notes that international characters are only supported after the @ symbol. Klaviyo rejects addresses containing characters like parentheses, commas, colons, semicolons, brackets, slashes, or spaces. Hard bounces are worse than a rejected row: HubSpot drops hard-bounced contacts from future marketing sends to protect your sending reputation.
- Inconsistent name capitalisation breaks personalisation. A single Name column of "SARAH CHEN", "sarah chen", and "Chen, Sarah" produces "Hi SARAH," in the subject line, and a blank first name renders as nothing at all unless you have set a default merge value. Mailchimp's *|FNAME|* tag only works when there is data in the field it maps to.
- SMS columns fail on the country code. Klaviyo requires the country for every imported phone number — either a Country column or the code inside the number itself — and its API accepts only E.164. A column of (555) 010-9999 and 555.010.9999 will not import as SMS-consented contacts.
- The privacy problem with fixing any of this: the obvious move is to paste the subscriber list into a free online cleaner, which makes that vendor a processor. GDPR Article 28(1) says a controller must use only processors that provide sufficient guarantees of appropriate technical and organisational measures — a bar a random web form has not cleared.
What you can do in Sigmera
Lowercase every address, trim the leading and trailing whitespace that survived a copy-paste, and flag values that do not match the basic email shape. That is the exact set of problems Mailchimp tells you to fix in the file rather than discover during the import — and Sigmera checks format only, never connecting to a mail server, so it will not claim an inbox exists.
You stacked a webinar list, a Shopify export, and a referral sheet into one CSV and the total looks suspiciously high. Deduplicating on the normalised email column collapses the repeats before they inflate your contact count and before two segments mail the same person the same campaign.
Your form captured one Name field and your ESP wants first and last name separately for *|FNAME|* personalisation. Splitting the column in a dedicated tool handles middle names and compound surnames that a LEFT/RIGHT formula mangles, and you see every row before you download.
Before uploading SMS-consented contacts, rewrite the whole phone column to a plus sign, country code, and national digits with no separators. Klaviyo requires country information on every imported number and accepts only E.164 over its API, so the format has to be right in the file.
The importer wants one Location field; your export has separate City and Country columns. Joining them gives the file the shape the template asks for without renaming the heading row your ESP is strict about.
Your list lives in .xlsx and the importer wants .csv. Converting in the browser produces UTF-8 output, so accented subscriber names arrive intact instead of as garbled characters in every personalised subject line you send them.
Sources
- 1.Format Guidelines for Your Import File — Mailchimp
- 2.Troubleshooting Contact Imports — Mailchimp
- 3.About Your Contacts — Mailchimp
- 4.About Mailchimp Pricing Plans — Mailchimp
- 5.Set Default Merge Values for an Audience — Mailchimp
- 6.Accepted phone number formats for SMS in Klaviyo — Klaviyo Help Center
- 7.Troubleshooting list imports — Klaviyo Help Center
- 8.Clean up contacts to improve email deliverability — HubSpot
- 9.Email bounce types — HubSpot
- 10.Art. 28 GDPR — Processor
Frequently asked questions
- Does Sigmera verify that an email address actually receives mail?
- No, and that distinction matters. Sigmera checks format — whether a value has a local part, an @, a domain, and a dot — then lowercases, trims, and can drop case-insensitive duplicates in one pass. It does not connect to mail servers, so it cannot tell you whether a mailbox is live. Format cleaning removes the addresses that would be rejected at import; a verification service is a separate step if you need mailbox-level confidence, and that step does involve sending your list to a third party.
- Why do duplicate subscribers cost me money?
- Because ESP pricing is usually a function of how many contacts you store. Mailchimp counts subscribed, unsubscribed, and non-subscribed contacts toward your monthly contact limit, and states that if your contact total goes beyond your limit at any point in the billing cycle you will see an additional charge on your bill rather than an interruption. Every duplicate that lands in the audience is a paid record that also risks sending the same person the same campaign twice.
- Is it GDPR-safe to clean a subscriber list this way?
- Cleaning a subscriber list is processing under GDPR, and it stays processing wherever you do it. What changes is who else touches the data. Sigmera reads and rewrites the file with JavaScript running in your own browser, so no vendor receives it and no processor relationship is created. Sending the same list to a cloud cleaner would make that vendor a processor, and Article 28(1) requires a controller to use only processors offering sufficient guarantees of appropriate technical and organisational measures. Browser-side cleaning removes that link from the chain. You are still the controller, and your lawful basis, consent records, and retention duties are unchanged.
- What formatting problems actually cause an import to fail?
- Mostly unremarkable ones. Mailchimp asks you to check the email column for syntax errors, unsupported characters, and extra spaces, and supports international characters only after the @ symbol. Klaviyo skips rows with no email or phone number, skips repeated addresses, and rejects emails containing characters such as parentheses, commas, colons, semicolons, brackets, slashes, or spaces. Both platforms trip over CSVs from European spreadsheet settings that use semicolons instead of commas as the delimiter.
- How should phone numbers be formatted for an SMS import?
- Include the country. Klaviyo accepts several written formats — E.164 like +12345678900, hyphenated, spaced, RFC3966, and E.123 notation — but requires country information on every number, usually via a Country column, and accepts only E.164 through its API. Normalising the whole column to E.164 before you upload satisfies every one of those paths and makes phone-based duplicate matching work at the same time.
- Will cleaning my list fix a high bounce rate?
- Partly. Removing malformed addresses stops the bounces caused by typos and broken syntax, which is real. It does not fix the bounces caused by abandoned mailboxes or contacts you should never have mailed. HubSpot's guidance on that side is suppression and deletion — segment out contacts who have not opened despite several campaigns, and delete contacts from purchased, guessed, or appended lists. Hard bounces are treated as permanent, and HubSpot excludes those contacts from future marketing sends to protect your reputation.
- How big a list can Sigmera handle, and do I need an account?
- There is no row or file-size cap on any plan — the ceiling is your own machine's memory, since nothing is queued against an upload limit. No install either: the tools run in a modern browser. You can preview any cleanup free and unlimited; a free account covers three downloads a month, with paid plans above that.